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Light fighter

A light fighter or lightweight fighter is a fighter aircraft towards the low end of the practical range of weight, cost, and complexity over which fighters are fielded. The light or lightweight fighter retains carefully selected competitive features, in order to provide cost-effective design and performance.

A well-designed lightweight fighter is able to match or better a heavier type plane-for-plane in many missions,  and for lower cost. The lightweight class can therefore be strategically valuable.

In attempts to scale this efficiency to still lower cost, some manufacturers have in recent years adopted the term “light fighter” to also refer to light primarily air-to-ground attack aircraft, some of which are modified trainer designs. These lower cost lightweight attack aircraft have become known as light combat aircraft (LCA's), and are sometimes considered to include some multirole light fighters.

From 1926 the light fighter concept has been a regular thread in the development of fighter aircraft, with some notable designs entering large-scale use.

Design aims
A key design goal of light/lightweight fighter design is to satisfy standard air-to-air fighter effectiveness requirements at minimum cost. These criteria, in order of importance, are the ability to benefit from the element of surprise, to have numerical superiority in the air, to have superior maneuverability, and to possess adequate weapon systems effectiveness. Light fighters typically achieve a surprise advantage over larger aircraft due to smaller visual and radar signatures, which is important since in the majority of air-to-air kills, the element of surprise is dominant. Their comparative lower cost and higher reliability also allows for greater numbers per budget. Finally, while a single engine light fighter would typically only carry about half the weapons load of a heavy twin engine fighter, its surprise and maneuverability advantages often allow it to gain positional advantage to make better use of those weapons.

A requirement for low cost and therefore small fighters first arose in the period between World War I and World War II. Examples include several RAF interceptor designs from the interwar era and French "Jockey" aircraft of the immediate pre-World War II. None of these very light fighters enjoyed success into World War II, as they were too hampered in performance. Similar to the meaning of lightweight fighter today, during World War II the term “small fighter” was used to describe a single engine aircraft of competitive performance, range, and armament load, but with no unnecessary weight and cost.

Effectiveness
The modern view of light/lightweight fighters is as a capable weapon intended to satisfy the main criteria of air-to-air combat effectiveness,    which in order of importance, are:

1. Superiority in the element of surprise, to be aware of the enemy before they are aware of you. In past combats, surprise advantage has been mostly based upon small visual and radar signatures, and having good visibility out of the cockpit. Surprise is a significant advantage, since historically in about 80% of air-to-air kills, the victim was unaware of the attacker until too late.

Small fighters like the F-5 with a planform area of about 300 sqft or the F-16 at about 400 sqft, compared to about 1050 sqft for the F-15, have a much lower visual profile. The small fighter is typically invisible to opposing pilots beyond about 4 mi, whereas a larger fighter such as the F-15 is visible to about 7 mi. This is a non-linear advantage to the light fighter opposing a heavy fighter. Additionally, smaller targets take longer to visually acquire even if they are visible. These two factors together give the light fighter pilot much better statistical odds of seeing the heavy fighter first and setting up a decisive first shot. Once the small fighter sees and turns towards the opponent its very small frontal area reduces maximum visual detection range to about 2 to 2.5 mi.

Given similar technology, smaller fighters typically have about two thirds the radar range against the same target as heavy fighters. However, this cannot be counted upon to give the large fighter a winning advantage, as larger fighters with typical radar cross sectional area of about 10 m2 are detectable by a given radar at about 50% farther range than the 2 to 3 m2 cross section of the light fighter. This approximately balances these trade-offs, and can sometimes favor the lightweight fighter. For example, from the front the F-15 actually presents about 20 m2 radar cross sectional area, and has been typically defeated by opposing F-16 forces not only in close dogfighting combat, but also in extensive Beyond Visual Range (BVR) trials. Also, airborne fighter radars are limited: their coverage is only to the front, and are far from perfect in detecting enemy aircraft. Although radar was extensively used by the United States in the Vietnam War, only 18% of North Vietnamese fighters were first detected by radar, and only 3% by radar on fighter aircraft. The other 82% were visually acquired.

The modern trend to stealth aircraft is an attempt to maximize surprise in an era when Beyond Visual Range (BVR) missiles are becoming more effective than the quite low effectiveness BVR has had in the past.

2. Numerical superiority in the air, which implies the need for lower procurement cost, lower maintenance cost, and higher reliability. Not even taking into account the sometimes superior combat capability of lighter aircraft based on surprise and maneuverability, the pure numbers issue of lower cost and higher reliability (higher sortie rates) also tends to favor light fighters. It is a basic outcome of Lanchester's laws, or the salvo combat model, that a larger number of less-sophisticated units will tend to be successful over a smaller number of more advanced ones; the damage dealt is based on the square of the number of units firing, while the quality of those units has only a linear effect on the outcome. This non-linear relationship favors the light and lightweight fighter.

Additionally, as pilot capability is actually the top consideration in maximizing total effectiveness of the pilot-aircraft system, the lower purchase and operational cost of light fighters permits more training, thus delivering more effective pilots. For example, as of 2013, total heavy F-15C operating cost is reported at US$41,900 per hour, and light F-16C cost at US$22,500 per hour.

3. Superior maneuverability, which in maneuvering combat allows getting into superior position to fire and score the kill. This is a function of achieving lower wing loading, higher thrust to weight ratio, and superior aerodynamics. This is sometimes described colloquially as “wrapping the smallest possible airframe around the most powerful available engine.” Professional analysis through 4th generation fighters shows that among heavier fighters only the F-15 has been generally competitive with lighter fighters, and its maneuvering performance is exceeded by several lighter fighters such as the F-16. Light fighters have no inherent aerodynamic advantage for speed and range, but when designed to be as simple as possible they do tend to have lower wing loading and higher thrust to weight ratio. Additionally, smaller fighters are lower in inertia, allowing a faster transient response in maneuvering combat.

4. Weapon systems effectiveness. This area is one where the light fighter can be at a disadvantage, since the combat load of a single engine light fighter is typically about half of a twin engine heavy fighter. However, modern single engine light fighters such as the General Dynamics F-16 Fighting Falcon and the Saab JAS 39 Gripen generally carry similar cannon and air-to-air missile fighter weapons as heavier fighters. Actual aerial combat in the modern era is of short duration, typically about two minutes, and as only a small fraction of this is spent actually firing, modest weapons load outs are generally effective. The ideal weapons load for a modern fighter is considered to be an internal gun and two to four guided missiles, a load that modern light fighters are fully capable of while maintaining high agility. For example, the JAS 39 Gripen, despite being the lightest major fighter in current production, carries a combat load of a 27mm cannon and up to six air-to-air missiles of the same types as carried by heavy fighters. Additionally, combat experience shows that weapons systems "effectiveness" has not been dominated by the amount of weaponry or "load out", but by the ability to achieve split second kills when in position to do so.

Concept summary
Superior technology has often been quoted as a strong factor favoring the heavy fighter. The specific argument usually presented is that heavy fighters have superior radar range and longer range BVR missiles that take advantage of that range. This radar range advantage is one of the major reasons for the existence of the modern heavy fighter, but it has not turned out to be a significant advantage in air combat history to date for several reasons. A major reason has been because long range BVR missile shots have often been unusable, and often unreliable when they could be taken. The weight of the larger missiles also reduces performance and range needed to get in position to fire. Due to these factors, between 1958 and 1982 in five wars there were 2,014 missile firings by fighter pilots engaged in air-to-air combat, but there were only four beyond-visual-range kills.

The more general and often misunderstood argument for more technology that has been historically assumed to favor heavy fighters is not just better radar but better systems support for the fighter pilot in other ways as well. Examples include all weather capability, precise electronic navigation, electronic counter-measures, data-linking for improved information awareness, and automation to lighten pilot workload and keep the pilot focused on tasks essential to combat. This was a compelling argument, as the greatest factor in the effectiveness of a fighter plane has always been the pilot. Quoting a prominent reference, "Throughout the history of air combat, a few outstanding fighter pilots, typically less than five percent of the whole, have run up large scores at the expense of their less gifted brethren. The numerical imbalance was such that a large number of high scorers was needed. The quest was on to turn each fighter pilot into an ace, and technology seemed the easiest, and the only way to achieve it. This was the idea underlying the first two American superfighters; the F-14 Tomcat and the F-15 Eagle.”

While the technology advantage for heavy fighters that better supported the pilot may well have been a valid point in the 1970s (when the F-14 and F-15 first entered service), this advantage has not been maintained over time. Engine performance improvements have improved load carry capability, and with more compact electronics, the lightweight fighter has, from the 1980s onwards, had similar pilot enhancing technical features. The lightweight fighter carries equally effective weapons including BVR missiles, and has similar combat range and persistence. The modern lightweight fighter achieves these competitive features while still maintaining the classic advantages of better surprise, numbers, and maneuverability. Thus, the lightweight fighter natural advantages have remained in force despite the addition of more technology to air combat.

Due to their lower costs, modern light fighters equip the air forces of many smaller nations. However, as budgets have limits for all nations, the optimum selection of fighter aircraft weight, complexity, and cost is an important strategic issue even for wealthy nations. The budgetary and strategic significance of light fighters is illustrated by the defense investment at stake. As an example where well referenced data is available, though numerous trial and combat references consider the lightweight F-16 to be as good or better on a per plane as the excellent but expensive F-15, fielding and maintaining a light fighter force based on the F-16 is approximately half the cost of the same number of F-15's. The US Air Force reports the total loaded cost per hour (as of 2013) of operating the F-16C to be ~US$22,500 per hour, while that of the heavy F-15C is $41,900 per hour. Numerous authoritative sources report that it takes about 200 to 400 flight hours per year to maintain fighter pilot proficiency.

Lanchester's laws on military superiority suggest that any technical superiority of the heavy fighter on a unit basis will not always translate to winning wars. For example, late in WWII the greatly superior German Messerschmitt Me 262 jet fighter, flown by the finest pilots Germany had left, many of them very high scoring aces with kill counts far in excess of Allied pilots, in its relatively small numbers suffered heavy losses and was unable to fundamentally alter the air war over Germany. Such issues are relevant to future military planning and deployments.

Interwar period
The light fighter class originally stemmed from concern at the growing size and cost of the frontline fighters in the 1920s. During the late 1920s and 1930s the light fighter would receive significant attention, especially in France.

One early light fighter project was the French Air Force's 'Jockey' interceptor program of 1926. Several aircraft, including the Nieuport-Delage NiD 48 and Amiot 110, were trialed without much success as they offered little over aircraft already in production In the late 1920s the British similarly issued specification F.20/27 for a short-range fast-climbing daylight interceptor. The de Havilland DH.77 and Vickers Jockey monoplanes were among seven designs tendered to meet the specification but neither went into production, the heavier but faster biplane Hawker Fury being preferred.

Despite the failure of their Jockey program, the French returned to lightweight fighters during the 1930s as a means to expand France's fleet of aircraft and counter the buildup of the German air force. This focused on light wooden fighters that could be built quickly without affecting production of other aircraft. A mid-thirties specification requiring fixed undercarriage produced two prototypes and in 1936 a revised requirement for retractable gear resulted in three prototypes. The most numerous of the two designs which went into production was the Caudron C.714. Delivery began in early 1940, but less than 100 had been built before the fall of France. Although underpowered, it was of necessity used by Polish air force pilots serving in France.

WWII
There was debate before and during World War II about the optimum size, weight and number of engines for fighter aircraft. During the war, fighters in the light to middle-weight range proved to be the most effective. Properly designed with competitive power to weight and thrust to drag ratios, these aircraft out-performed heavy fighters in combat due to greater surprise and maneuverability. They were also more cost effective, allowing greater numbers to be deployed as a combat advantage. Some single-engined fighters (including the P-51 Mustang and A6M Zero) could also match or beat the range of their heavy twin-engined counterparts.

Germany
The German Messerschmitt Bf 109 entered service in 1937 as a high speed interceptor and became the most-produced fighter in history, with nearly 34,000 built. The design philosophy of the Bf 109 was to wrap a small airframe around a powerful engine using Messerschmitt's "lightweight construction" principle, which aimed to minimize the weight and number of separate parts in the aircraft. By concentrating wing, engine and landing gear weight in the firewall, the structure of the Bf 109 could be made relatively light and simple. The Bf 109 was the second-smallest major fighter aircraft of World War II and the lightest in the European theater. The "E" version used in the Battle of Britain had an empty weight of 2,010 kg. The more heavily armed and powerful G version used later in the war had an empty weight of 2,700 kg. In comparison, its main fighter opponents weighed 2,100 to 5,800 kg.

Japan
The lightest major fighter of World War II was the Japanese Mitsubishi A6M Zero naval fighter. Entering service in 1940 and remaining in use throughout the war, it had an empty weight of 1,680 kg for the A6M2 version, which was extremely light even by the standards of its time. The design team leader, Jiro Horikoshi, intended it to be as light and agile as possible, embodying the qualities of a samurai sword. With Japanese engine technology lagging behind that of the west, but required to out-perform western fighters, the designers minimised weight to maximize range and maneuverability. This was achieved by methods including the use of light weaponry and the absence of armour and self-sealing fuel tanks. Early in World War II the Zero was considered the most capable carrier-based fighter in the world, and the extremely long range meant that the Zero could appear in and strike locations where Japanese air power was otherwise not expected to reach. In early combat operations, the Zero gained a reputation as an excellent dogfighter, achieving a kill ratio of 12 to 1. However, Japan was unable to keep improving the aircraft through the war, primarily limited by lagging engine technology, and by mid-1942 a combination of new tactics and the introduction of better aircraft enabled the Allied pilots to engage the Zero on equal or superior terms. For instance, the larger and heavier Grumman F6F Hellcat had superior performance to the Zero in all aspects other than manoeuvrability. Combined with the US Navy's superior training standards, units equipped with the type achieved a large victory-to-loss ratio against the Zero and other Japanese aircraft.

United Kingdom
The Royal Air Force entered World War II with two modern single-engined fighters forming the majority of the fighter force of the RAF – the Supermarine Spitfire and the Hawker Hurricane. Initially introduced as bomber interceptors, both started with eight machine gun armament but changed to cannons in the course of the war.

The Spitfire, designed by R. J. Mitchell, entered service in 1938 and remained in production throughout the war. The empty weight of the Battle of Britain-era Spitfire IIA was 2,142 kg, increasing to 2,984 kg in a later variant. It was highly maneuverable and was generally a match for its German opponents. Most Spitfires had a Rolls-Royce Merlin engine, but later variants used one of the most powerful engines of the war – the Rolls-Royce Griffon. The Spitfire was produced and improved throughout the war but was complex to build and had limited range. In other respects it was considered an outstanding fighter.

The Hawker Hurricane played an important role in the Battle of Britain, but its performance was inferior to the Spitfire and during the war was removed from frontline duty as a fighter and used for ground attack. Production ceased in mid-1944. The Hurricane IIC weighed 2,605 kg empty.

United States
On the eve of the war, the United States Army Air Corps contracted for several "very light" fighter designs based on the Ranger V-770 engine, an air-cooled inverted V12 engine, that delivered up to 700 hp. Two prototypes were the Bell XP-77 (empty weight 2,855 lb) and the Douglas XP-48 (empty weight 2,655 lb). Problems with the engine and performance and a perceived lack of need saw both programs canceled. However, they were specifically defined as "light" or "very light" fighter aircraft.

Instead, the US developed a number of standard pursuit fighters, the most efficient being the relatively lightweight North American P-51 Mustang. The P-51 was more economical, costing less per air-to-air kill than any other American aircraft.

The United States Navy, also made aware of lightweight advantages by combat results, ordered a lighter version of the Grumman F6F Hellcat, which at 9,238 lb empty weight had limited maneuverability and rate of climb. The planned Grumman F8F Bearcat replacement used the same engine, but with empty weight reduced to 7,070 lb had excellent performance. It entered production too late to see combat in World War II. Postwar, it equipped 24 fighter squadrons in the Navy and a smaller number in the Marines. Navy author James Perry Stevenson called the Bearcat "the quintessential lightweight fighter".

USSR
The Soviet Yakovlev Yak-3, which entered service in 1944, was an attempt to develop the smallest and lightest fighter around the 1,600 hp V-12 Klimov M-107 engine. As this engine was not available in time, the 1,300 hp Klimov M-105 was substituted, with a resulting empty weight of 2,100 kg. Despite the reduced power, the Yak-3 had a top speed of 655 km/h. The Yak-3 could out-turn the German Bf 109 and Fw 190. German pilots were ordered to avoid dogfights with the Yak-3 at low level.

The Soviet Yakovlev Yak-9 was also a lightweight fighter, initially using the M-105 engine. With an empty weight 2,350 kg, it was among the lighter major fighters of World War II. A development of the Yakovlev Yak-7, it entered combat in late 1942 and was the Soviet Union's most-produced fighter with 16,769 built. At low altitudes, the Yak-9 was faster and more maneuverable than the Bf 109. However, its armament of one cannon and one machine gun was relatively light.

Early jet age
The Luftwaffe's Heinkel He 162 Volksjäger of 1945 was a very deliberate attempt at producing a low cost jet fighter without materials that were in short supply at the end of the war. It was a low cost emergency fighter, one of several designs for the Emergency Fighter Program using rockets or jets, which could be built by unskilled labour and would be flown by inexperienced pilots to defend the Third Reich. With an empty weight of 1660 kg, it was very light even for the time. The He 162A was powered by a BMW 003 engine. With a top speed of 790 km/h at normal thrust at sea level, and 840 km/h at 6000 m, it was about 130 km/h faster than Allied fighters but had no more than 30 minutes fuel. Test pilots reported it to be a fine handling and conceptually well designed aircraft, and considered its problems to be rushed delivery more than any fundamental design flaws. It never formally entered operational service, and did not receive the benefit of being flown by well trained pilots using a well considered operational plan. Only 120 were delivered to units, and it scored only a few kills in experimental use before the war ended.

After World War II fighter design moved into the jet era, and many jet fighters followed the successful World War II formula of highly efficient mostly single-engine designs. Prominent early examples include the British mid-50s Folland Gnat, the American North American F-86 Sabre, Northrop F-5 and the Soviet Mikoyan MiG-15.

The Mikoyan-Gurevich MiG-15 was a Soviet jet fighter developed shortly after World War II. It weighed 3,630 kg empty and was one of the first successful jet fighters to use swept wings for high transonic speeds. It first saw service in the Chinese Civil War. In combat during the Korean War, it outclassed straight-winged jet day fighters. Some 18,000 were produced.

The North American F-86 Sabre, a transonic jet fighter manufactured from 1949, was the United States's first swept wing fighter. With an empty weight of 5000 kg it was nearly 40 per cent heavier than the MiG-15, but light compared with today's fighters. The F-86 had a bubble canopy, small size, moderate cost, high maneuverability, and an armament of six .50 in calibre machine guns. It could turn faster than any modern fighter. It saw combat against the Mig 15 in high-speed dogfights during the Korean War. Considered (with the MiG 15) as one of the best fighters in the Korean War, it was the most-produced Western jet fighter, with total production of 9,860 units. It continued as a front-line fighter in numerous air forces until 1994.

The Folland Gnat was a British private venture design for a light fighter and was the product of "Teddy" Petter's theories about fighter aircraft design. Although only adopted by the UK as a trainer, the Gnat served successfully as a fighter for the Indian Air Force and was in service from 1959 to 1979. India produced an improved derivative of it, the HAL Ajeet. With an empty weight of 2,177 kg it was the lightest successful post-World War II jet fighter, though at the cost of shorter range compared to other fighters. The Gnat is credited as having shot down seven Pakistani F-86s in the 1965 war, for the loss of two Gnats downed by PAF fighters. During the Indo-Pakistani War of 1971, Indian Gnats shot down several Pakistani F-86s without loss. The Gnat was successful against the capable F-86 flown by well-trained Pakistani pilots because its smaller size allowed a superior level of surprise and greater agility in dogfighting.

In the early 1950s, the NATO NBMR-1 competition for a cheap "light weight tactical strike fighter" able to carry conventional or tactical nuclear weapons and operate from dispersed airfields with minimum ground support led to designs including the French SNCASE Baroudeur, Breguet Taon and Dassault Étendard VI, the Italian Aeritalia G.91 and Aerfer Ariete. Other competitors included the Northrop F-5A. The British chose to continue production of the Hawker Hunter, while the French decided to work independently of the competition. Italy produced the Fiat G.91 while the competition was underway and, in 1957, this was selected as NATO's standard strike fighter. With an empty weight of 3,100 kg it was very light for a jet fighter. The G.91 entered service with the Italian Air Force in 1961, with the West German Luftwaffe, in 1962, and later with the Portuguese Air Force. It was in production for 19 years, with production ceasing in 1977 with 756 aircraft built.

In the mid-1950s, it was realized that fighter costs were escalating to possibly unacceptable levels, and some companies sought to reverse the trend to heavier and more expensive fighters. A prominent result was the Mach 1.3 to Mach 1.6, 4335 kg Northrop F-5. Smaller, cheaper and simpler than the contemporary F-4 Phantom, the F-5 had excellent performance and was popular on the export market. It was perhaps the most effective US-produced fighter in the 1960s and early 1970s, with a high sortie rate, low accident rate, high maneuverability, and an effective armament of 20mm cannon and heat-seeking missiles. Though the United States never procured the F-5 for main line service, it did adopt it as an opposing forces (OPFOR) "aggressor" for dissimilar training role because of its small size and similarity in performance to the Soviet MiG-21. It also participated in large scale trials of aircraft and missile effectiveness. In the extensive 9 month long AIMVAL/ACEVAL trial at Nellis AFB in 1977, the F-5 "Red Force" was quite effective against the considerably larger F-14 Tomcat naval fighter and F-15 Eagle single seat fighters making up the "Blue Force". These modern aircraft are approximately five to ten times more expensive than the various versions of the F-5. The final result was the F-5 fighting the more modern fighters to an effective plane for plane draw. In direct combat against the similar MiG-21 (which performed well against American fighters in Vietnam), the F-5 is known to have scored 13 victories against 4 losses. Just under 1000 of the F-5A Freedom Fighter were sold worldwide, and another 1,400 of the updated F-5E Tiger II version. As of 2016 the F-5 remains in service with many nations, some of which have undertaken extensive upgrade programs to modernize its abilities with digital avionics and radar guided missiles.

The light middleweight Saab 35 Draken was a second to third generation Mach 2 fighter produced from 1955 to 1974 and in service for 45 years, with empty weights from 6,577 kg (14,500) to 7,440 kg. It was a double-delta wing single-engine fighter. Its steeply swept inner delta wing allowed for a high cruise speed. The double-delta, with a shallower rake at the outer wing, improved maneuverability. It was designed to be cheap enough for small countries and simple enough to be maintained by conscripted mechanics. Its high acceleration, light wing loading, and extreme maneuverability enabled it to be an excellent dogfighter. However, it had an overly complex fire control system. It remained in service until 2005.

The French Dassault Mirage III is another late 2nd/early 3rd generation delta wing Mach 2 fighter. Stemming from a French requirement for a lightweight all-weather interceptor, it has been in service since 1961. With an empty weight of 7,076 kg in the "E" version with added ground attack capability, the Mirage III is a light fighter by modern standards (though twice as heavy as initial Mirage I ). Its maneuverability, modest cost, reliability and armament of 30mm cannons and heat seeking missiles proved effective. It served the French Air Force and was exported to many countries. It performed very well for Israel in the Six-Day War of 1967 and Yom Kippur War of 1973. However, Argentina's Mirage IIIs were out-performed by British Sea Harriers during the Falklands War of 1982.

Similar in size to the F-5, the Russian Mikoyan-Gurevich MiG-21 entered service in 1959, was produced until 1985, and is still in widespread use today. The late Generation 2 to Generation 3, Mach 2 MiG-21 has an empty weight of 4535 kg, and has served nearly 60 nations. It shot down 37 to 104 US Phantoms, in the Vietnam War, with the Phantoms shooting down 54 to 66 MiG-21s in return. In December 1966 the MiG-21 pilots of the 921st FR downed 14 F-105s without any losses. Its weaknesses include poor visibility and relatively short range, but has otherwise proven to be a capable fighter.

The US's Vought F-8 Crusader used in Vietnam weighed 8000 kg, as compared with 13,750 kg for an F-4 Phantom. It was a simple, supersonic, single engine, gun- and heat-seeker armed fighter in front-line service from 1957 to 1976. It had no radar except a simple ranging gunsite radar. The US claims the Crusader (up to 1968) shot down six enemy aircraft for every loss, compared with 2.4 for every Phantom lost. The three F-8s shot down in air-to-air were all lost to MiG-17 cannon fire.

The first few decades of the jet fighter era showed a combat history similar in general trend to that of the propeller fighters of World War II. So long as lighter fighters are of sufficient power-to-weight ratio and airframe sophistication, and flown by similarly skilled pilots, they tend to dominate over heavier fighters using surprise, numbers, and maneuverability. However, one significant difference did emerge in design strategy in the early jet fighter era. In World War II fighter design was strongly influenced by the seeking of higher speeds that were valuable in combat in order to close with the enemy or to escape. This trend was instinctively continued in some jet fighters through the 3rd generation (F-4 at Mach 2.23) and into the 4th generation (F-14 at Mach 2.35 and F-15 at Mach 2.5+). The aerodynamic requirements to operate at such speeds add considerable complexity, weight, and cost to the airframe. But, these Mach 2 and above class speeds have zero utility in combat. Combat speeds never exceed Mach 1.7 and seldom 1.2, for two reasons. First, it requires extensive use of the afterburner, which typically increases fuel consumption by about a factor of three or even four, and rapidly reduces operational radius. Second, speeds even above about Mach 0.7 to Mach 1 (depending on circumstances) so widen the turn radius in maneuvering combat that the fighter is thrown too wide to get a tracking solution on an opponent. Speed had reached the limit of its practical combat value, such that optimum fighter design required understanding the penalties the endless search for higher speed was imposing, and sometimes deliberately choosing not to accept those penalties.

Supersonic era
As supersonic performance, with afterburning engines and modern missile armament, became the norm the Soviet Mikoyan MiG-21, the French Mirage III, and the Swedish Saab Draken entered service. The next generation of lightweight fighters included the American F-16 Fighting Falcon, Swedish JAS 39 Gripen, Indian HAL Tejas, Korean FA-50, Japanese Mitsubishi F-2, Chinese Chengdu J-10 and Pakistani CAC/PAC JF-17 Thunder. The high practical and budgetary effectiveness of modern light fighters for many missions is why the US Air Force adopted both the F-15 Eagle and F-16 in a "hi/lo" strategy of both an outstanding but expensive heavy fighter and a lower cost but also outstanding lightweight fighter. The investment to maintain a competitive modern lightweight fighter air force is approximately $90M to $130M (2013 dollars) per plane over a 20-year service life, which is approximately half the cost of heavy fighters so understanding fighter aircraft design trade-offs and combat effectiveness is of national level strategic importance.

In the 1960s and 1970s, a US-based "Fighter Mafia", led by colonels John Boyd, Everest "Rich" Riccione and analyst Pierre Sprey advocated for production of a 4th generation light fighter. Despite heavy fighter losses in the Vietnam War, most senior US Air Force leaders still opposed the light fighter concept. After much debate, General Dynamics designed the successful F-16. Its competitor, the Northrop YF-17, led to the successful McDonnell Douglas F/A-18 Hornet Navy fighter as a cheaper alternative to the F-14. The F-16 offered excellent air-to-air combat performance due partly to its fly-by-wire control system, which improved agility. When not burdened by heavy air-to-ground weapons, the F-16 had the longest range of any US fighter at the time. The F-16 and F/A-18 later added significant weight to become multirole fighters with strong air-to-ground capabilities, pushing them towards the "middleweight" range of modern fighters.

The Soviet counterpart to the F-16 and F/A-18, the Mikoyan MiG-29, was originally part of the Perspektivnyy Lyogkiy Frontovoy Istrebitel (LPFI, or "Advanced Lightweight Tactical Fighter") program.

In the 1980s the privately developed F-5G, later renamed the Northrop F-20 Tigershark, aimed to correct weaknesses in the aging F-5 while maintaining small size and low cost. Its empty weight was 6,000 kg. Its General Electric F404 engine produced 60 per cent more power than the F-5, and it had a higher climb rate and acceleration, better cockpit visibility, and more modern radar. Chuck Yeager, test pilot and the first man to break the sound barrier, referred to the F-20 as "the finest fighter" of the mid-1980s. Despite its high performance and cost effectiveness, the F-20 lost out for foreign sales against the similarly capable, more expensive F-16, which was being procured in large numbers by the US Air Force and was viewed as having greater support. The Tigershark was cancelled having made no sales. The HAL Tejas has an empty weight of 6,500 kg, and is the lightest fighter among current production light fighters. Introduced into limited service in 2014, with 16 IOC specification aircraft delivered to January 2020, it was the lowest-cost fighter aircraft with competitive air-to-air capability in production at that time, at an equivalent cost of US$27 million. 83 Tejas MK1As are ordered, with another 100 planned, making it the lightest 4.5 generation aircraft in production. The design is similar to the Mirage III and JAS 39 Gripen, being a light tailless delta-wing single-engine fighter with ground attack capability.

The French Dassault Mirage 2000 was designed for the French Air Force (Armée de l'Air) in the late 1970s, as a lightweight single-engine fighter. Based on the Mirage III, it entered service in 1982, and has since evolved into a multirole aircraft. In heavier multirole form, it has empty weight of 7,400 kg. More than 600 were built and it has served in the air forces of nine nations.

South Korea's KAI T-50 Golden Eagle, designed by Lockheed Martin with Korea Aerospace Industries, is based on the F-16 multirole-fighter. Its latest variant, the FA-50 Fighting Eagle, is designated as a light fighter and trainer. It uses the same air frame as the T-50 advanced trainer introduced in August 2002. It is now deployed with South Korean Air Force and the Philippine Air Force.

The CAC/PAC JF-17 Thunder light fighter was developed jointly by China's Chengdu Aircraft Corporation and Pakistan's Pakistan Aeronautical Complex in the early 2000s. it was inducted into the Pakistan Air Force in February 2010. At least 66 aircraft have been delivered to Pakistan. More aircraft are scheduled to be introduced in 2018. A twin-seater variant was undergoing flight testing as of late 2015.

The JAS 39 Gripen is a single-engine light fighter manufactured by the Swedish aerospace company Saab. With an empty weight of 6,800 kg it is the second lightest fighter in production as of 2016. Though primarily an air superiority fighter, the design has effective air-to- ground capability as well. Its delta wing offers high cruise and super-cruise (above Mach 1 without using after-burner), low wing-loading and high maneuverability. It can operate from short airstrips and 800 m sections of road, can be serviced by moderately trained mechanics, and has high sortie rates. Among Western 4th generation fighters the Gripen has the lowest operating cost at about $4,700 per flight hour (as of 2012). The lowest operating cost in current range of fighters discussed above is of HAL Tejas of about $4,000. Among western fighters, next best operating cost fighter is the F-16 at about $7,000 per flight hour. The Gripen has relaxed stability fly-by-wire flight controls for maximum agility, a top speed of Mach 2, a 27mm cannon, heat-seeking missiles, and radar-guided missiles.

Current trends
The issue of where a fighter is best positioned on the weight, cost, and complexity curve is still a contentious issue. Stealth technology (airframe and engine design that strongly reduce radar and heat signatures) seeks to emphasize the most important feature of fighter effectiveness, the element of surprise. So far it has been featured only on heavier and more expensive fighters, specifically the F-22 Raptor and F-35 Lightning II. These fighters are not only stealthy, but also have information or combat awareness advantages due to active electronically scanned array (AESA) radars, and data linking for external cuing of enemy position and friendly force status. Their combination of near invisibility to conventional radars, superior combat awareness, networking, and reliable Beyond Visual Range (BVR) missiles, enables them to get deep inside the enemy's OODA loop and destroy enemy fighters before their pilots are even aware of the threat.

Fighter drones (see Unmanned combat aerial vehicle) are under development, driven by the same tactical and cost effectiveness principles of light fighters. Their perceived advantages include not only cost and numbers, but the fact that their software based "pilot" does not require years of training, is always at the same peak effectiveness for each aircraft (unlike the human pilot case where the top 5% of pilots have historically scored about 50% of all kills ), is not physiologically limited, and does not have a life to lose if the aircraft is lost in combat. Though there is cultural resistance to replacement of human fighter pilots and also concerns about entrusting life and death decisions to robot software, such fighter drones are expected to eventually be implemented.

title: Light fighter


text:
Hyperfine structure

In atomic physics, hyperfine structure is defined by small shifts in otherwise degenerate electronic energy levels and the resulting splittings in those electronic energy levels of atoms, molecules, and ions, due to electromagnetic multipole interaction between the nucleus and electron clouds.

In atoms, hyperfine structure arises from the energy of the nuclear magnetic dipole moment interacting with the magnetic field generated by the electrons and the energy of the nuclear electric quadrupole moment in the electric field gradient due to the distribution of charge within the atom. Molecular hyperfine structure is generally dominated by these two effects, but also includes the energy associated with the interaction between the magnetic moments associated with different magnetic nuclei in a molecule, as well as between the nuclear magnetic moments and the magnetic field generated by the rotation of the molecule.

Hyperfine structure contrasts with fine structure, which results from the interaction between the magnetic moments associated with electron spin and the electrons' orbital angular momentum. Hyperfine structure, with energy shifts typically orders of magnitudes smaller than those of a fine-structure shift, results from the interactions of the nucleus (or nuclei, in molecules) with internally generated electric and magnetic fields.

History
The first theory of atomic hyperfine structure was given in 1930 by Enrico Fermi for an atom containing a single valence electron with an arbitrary angular momentum. The Zeeman splitting of this structure was discussed by S. A. Goudsmit and R. F. Bacher later that year. In 1935, H. Schüler and Theodor Schmidt proposed the existence of a nuclear quadrupole moment in order to explain anomalies in the hyperfine structure of Europium, Cassiopium(older name for Lutetium), Indium, Antimony and Mercury.

Theory
The theory of hyperfine structure comes directly from electromagnetism, consisting of the interaction of the nuclear multipole moments (excluding the electric monopole) with internally generated fields. The theory is derived first for the atomic case, but can be applied to each nucleus in a molecule. Following this there is a discussion of the additional effects unique to the molecular case.

Magnetic dipole
The dominant term in the hyperfine Hamiltonian is typically the magnetic dipole term. Atomic nuclei with a non-zero nuclear spin $$\mathbf{I}$$ have a magnetic dipole moment, given by: $$\boldsymbol{\mu}_\text{I} = g_\text{I}\mu_\text{N}\mathbf{I},$$ where $$g_\text{I}$$ is the g-factor and $$\mu_\text{N}$$ is the nuclear magneton.

There is an energy associated with a magnetic dipole moment in the presence of a magnetic field. For a nuclear magnetic dipole moment, μI, placed in a magnetic field, B, the relevant term in the Hamiltonian is given by: $$\hat{H}_\text{D} = -\boldsymbol{\mu}_\text{I}\cdot\mathbf{B}.$$

In the absence of an externally applied field, the magnetic field experienced by the nucleus is that associated with the orbital (ℓ) and spin (s) angular momentum of the electrons: $$\mathbf{B} \equiv \mathbf{B}_\text{el} = \mathbf{B}_\text{el}^\ell + \mathbf{B}_\text{el}^s.$$

Electron orbital magnetic field
Electron orbital angular momentum results from the motion of the electron about some fixed external point that we shall take to be the location of the nucleus. The magnetic field at the nucleus due to the motion of a single electron, with charge –e at a position r relative to the nucleus, is given by: $$\mathbf{B}_\text{el}^\ell = \frac{\mu_0}{4\pi}\frac{-e\mathbf{v} \times -\mathbf{r}}{r^3},$$ where −r gives the position of the nucleus relative to the electron. Written in terms of the Bohr magneton, this gives: $$\mathbf{B}_\text{el}^\ell = -2\mu_\text{B} \frac{\mu_0}{4\pi}\frac{1}{r^3} \frac{\mathbf{r} \times m_\text{e}\mathbf{v}}{\hbar}.$$

Recognizing that mev is the electron momentum, p, and that r×p/ħ is the orbital angular momentum in units of ħ, ℓ, we can write: $$\mathbf{B}_\text{el}^\ell = -2\mu_\text{B}\frac{\mu_0}{4\pi}\frac{1}{r^3}\mathbf{\ell}.$$

For a many-electron atom this expression is generally written in terms of the total orbital angular momentum, $$\mathbf{L}$$, by summing over the electrons and using the projection operator, $$\varphi^\ell_i$$, where $\sum_i\mathbf{\ell}_i = \sum_i\varphi^\ell_i\mathbf{L}$. For states with a well defined projection of the orbital angular momentum, $L_{z}$, we can write $$\varphi^\ell_i = \hat{\ell}_{z_i}/L_z$$, giving: $$\mathbf{B}_\text{el}^\ell = -2\mu_\text{B} \frac{\mu_0}{4\pi} \frac{1}{L_z}\sum_i\frac{\hat{\ell}_{zi}}{r_i^3}\mathbf{L}.$$

Electron spin magnetic field
The electron spin angular momentum is a fundamentally different property that is intrinsic to the particle and therefore does not depend on the motion of the electron. Nonetheless it is angular momentum and any angular momentum associated with a charged particle results in a magnetic dipole moment, which is the source of a magnetic field. An electron with spin angular momentum, s, has a magnetic moment, μs, given by: $$\boldsymbol{\mu}_\text{s} = -g_s\mu_\text{B}\mathbf{s},$$ where gs is the electron spin g-factor and the negative sign is because the electron is negatively charged (consider that negatively and positively charged particles with identical mass, travelling on equivalent paths, would have the same angular momentum, but would result in currents in the opposite direction).

The magnetic field of a point dipole moment, μs, is given by: $$\mathbf{B}_\text{el}^s = \frac{\mu_0}{4\pi r^3} \left(3\left(\boldsymbol{\mu}_\text{s} \cdot \hat{\mathbf{r}}\right) \hat{\mathbf{r}} - \boldsymbol{\mu}_\text{s}\right) + \dfrac{2\mu_0}{3} \boldsymbol{\mu}_\text{s}\delta^3(\mathbf{r}).$$

Electron total magnetic field and contribution
The complete magnetic dipole contribution to the hyperfine Hamiltonian is thus given by: $$\begin{align} \hat{H}_D ={} &2g_\text{I}\mu_\text{N}\mu_\text{B} \dfrac{\mu_0}{4\pi}\dfrac{1}{L_z} \sum_i \dfrac{\hat{\ell}_{zi}}{r_i^3} \mathbf{I} \cdot \mathbf{L} \\ & {}+ g_\text{I}\mu_\text{N}g_\text{s}\mu_\text{B} \frac{\mu_0}{4\pi} \frac{1}{S_z}\sum_i \frac{\hat{s}_{zi}}{r_i^3} \left\{ 3\left(\mathbf{I} \cdot \hat{\mathbf{r}}\right)\left(\mathbf{S}\cdot\hat{\mathbf{r}}\right) - \mathbf{I}\cdot\mathbf{S}\right\} \\ & {}+ \frac{2}{3} g_\text{I}\mu_\text{N}g_\text{s}\mu_\text{B}\mu_0 \frac{1}{S_z}\sum_i\hat{s}_{zi}\delta^3{\left(\mathbf{r}_i\right)} \mathbf{I}\cdot\mathbf{S}. \end{align}$$

The first term gives the energy of the nuclear dipole in the field due to the electronic orbital angular momentum. The second term gives the energy of the "finite distance" interaction of the nuclear dipole with the field due to the electron spin magnetic moments. The final term, often known as the Fermi contact term relates to the direct interaction of the nuclear dipole with the spin dipoles and is only non-zero for states with a finite electron spin density at the position of the nucleus (those with unpaired electrons in s-subshells). It has been argued that one may get a different expression when taking into account the detailed nuclear magnetic moment distribution.

For states with $$\ell \neq 0$$ this can be expressed in the form $$\hat{H}_D = 2 g_I \mu_\text{B} \mu_\text{N} \dfrac{\mu_0}{4\pi} \dfrac{\mathbf{I}\cdot\mathbf{N}}{r^3},$$ where: $$\mathbf{N} = \boldsymbol{\ell} - \frac{g_s}{2} \left[\mathbf{s} - 3(\mathbf{s}\cdot \hat{\mathbf{r}})\hat{\mathbf{r}}\right].$$

If hyperfine structure is small compared with the fine structure (sometimes called IJ-coupling by analogy with LS-coupling), I and J are good quantum numbers and matrix elements of $$\hat{H}_\text{D}$$ can be approximated as diagonal in I and J. In this case (generally true for light elements), we can project N onto J (where $J = L + S$ is the total electronic angular momentum) and we have: $$\hat{H}_\text{D} = 2 g_I \mu_\text{B} \mu_\text{N} \dfrac{\mu_0}{4\pi} \dfrac{\mathbf{N}\cdot\mathbf{J}}{\mathbf{J}\cdot\mathbf{J}} \dfrac{\mathbf{I}\cdot\mathbf{J}}{r^3}.$$

This is commonly written as $$\hat{H}_\text{D} = \hat{A}\mathbf{I}\cdot\mathbf{J},$$ with $\left\langle\hat{A}\right\rangle$ being the hyperfine-structure constant which is determined by experiment. Since $I⋅J = 1⁄2{F⋅F − I⋅I − J⋅J}$ (where $F = I + J$ is the total angular momentum), this gives an energy of: $$\Delta E_\text{D} = \frac{1}{2}\left\langle\hat{A}\right\rangle[F(F + 1) - I(I + 1) - J(J + 1)].$$

In this case the hyperfine interaction satisfies the Landé interval rule.

Electric quadrupole
Atomic nuclei with spin $$I \ge 1$$ have an electric quadrupole moment. In the general case this is represented by a rank-2 tensor, $$Q_{ij}$$, with components given by: $$Q_{ij} = \frac{1}{e} \int\left(3x_i^\prime x_j^\prime - \left(r'\right)^2 \delta_{ij}\right)\rho{\left(\mathbf{r}'\right)} \, d^3\mathbf{r}',$$ where i and j are the tensor indices running from 1 to 3, xi and xj are the spatial variables x, y and z depending on the values of i and j respectively, δij is the Kronecker delta and ρ(r) is the charge density. Being a 3-dimensional rank-2 tensor, the quadrupole moment has 32 = 9 components. From the definition of the components it is clear that the quadrupole tensor is a symmetric matrix ($Q_{ij} = Q_{ji}$) that is also traceless ($\operatorname{tr} Q = \sum_i Q_{ii} = 0$ ), giving only five components in the irreducible representation. Expressed using the notation of irreducible spherical tensors we have: $$T^2_m(Q) = \sqrt{\frac{4\pi}{5}} \int \rho{\left(\mathbf{r}'\right)} \left(r'\right)^2 Y^2_m\left(\theta', \varphi'\right) \, d^3\mathbf{r}'. $$

The energy associated with an electric quadrupole moment in an electric field depends not on the field strength, but on the electric field gradient, confusingly labelled $\underline{\underline{q}}$, another rank-2 tensor given by the outer product of the del operator with the electric field vector: $$\underline{\underline{q}} = \nabla\otimes\mathbf{E},$$ with components given by: $$q_{ij} = \frac{\partial^2V}{\partial x_i \, \partial x_j}.$$

Again it is clear this is a symmetric matrix and, because the source of the electric field at the nucleus is a charge distribution entirely outside the nucleus, this can be expressed as a 5-component spherical tensor, $$T^2(q)$$, with: $$\begin{align} T^2_0  (q) &= \frac{\sqrt{6}}{2} q_{zz} \\ T^2_{+1}(q) &= -q_{xz} - i q_{yz} \\ T^2_{+2}(q) &= \frac{1}{2}(q_{xx} - q_{yy}) + iq_{xy}, \end{align}$$ where: $$T^2_{-m}(q) = (-1)^mT^2_{+m}(q)^*.$$

The quadrupolar term in the Hamiltonian is thus given by: $$\hat{H}_Q = -e T^2(Q) \cdot T^2(q) = -e\sum_m (-1)^m T^2_m(Q) T^2_{-m}(q).$$

A typical atomic nucleus closely approximates cylindrical symmetry and therefore all off-diagonal elements are close to zero. For this reason the nuclear electric quadrupole moment is often represented by $Q_{zz}$.

Molecular hyperfine structure
The molecular hyperfine Hamiltonian includes those terms already derived for the atomic case with a magnetic dipole term for each nucleus with $$I > 0$$ and an electric quadrupole term for each nucleus with $$I \geq 1$$. The magnetic dipole terms were first derived for diatomic molecules by Frosch and Foley, and the resulting hyperfine parameters are often called the Frosch and Foley parameters.

In addition to the effects described above, there are a number of effects specific to the molecular case.

Direct nuclear spin–spin
Each nucleus with $$I > 0$$ has a non-zero magnetic moment that is both the source of a magnetic field and has an associated energy due to the presence of the combined field of all of the other nuclear magnetic moments. A summation over each magnetic moment dotted with the field due to each other magnetic moment gives the direct nuclear spin–spin term in the hyperfine Hamiltonian, $$\hat{H}_{II}$$. $$\hat{H}_{II} = -\sum_{\alpha\neq\alpha'} \boldsymbol{\mu}_\alpha \cdot \mathbf{B}_{\alpha'},$$ where α and α' are indices representing the nucleus contributing to the energy and the nucleus that is the source of the field respectively. Substituting in the expressions for the dipole moment in terms of the nuclear angular momentum and the magnetic field of a dipole, both given above, we have $$ \hat{H}_{II} = \dfrac{\mu_0\mu_\text{N}^2}{4\pi} \sum_{\alpha\neq\alpha'} \frac{g_\alpha g_{\alpha'}}{R_{\alpha\alpha'}^3} \left\{ \mathbf{I}_\alpha\cdot\mathbf{I}_{\alpha'} - 3\left(\mathbf{I}_\alpha \cdot \hat{\mathbf{R}}_{\alpha\alpha'}\right)\left(\mathbf{I}_{\alpha'} \cdot \hat{\mathbf{R}}_{\alpha\alpha'}\right) \right\}. $$

Nuclear spin–rotation
The nuclear magnetic moments in a molecule exist in a magnetic field due to the angular momentum, T (R is the internuclear displacement vector), associated with the bulk rotation of the molecule, thus $$ \hat{H}_\text{IR} = \frac{e\mu_0\mu_\text{N}\hbar}{4\pi}\sum_{\alpha \neq \alpha'} \frac{1}{R_{\alpha\alpha'}^3} \left\{\frac{Z_\alpha g_{\alpha'}}{M_\alpha} \mathbf{I}_{\alpha'} + \frac{Z_{\alpha'}g_\alpha}{M_{\alpha'}} \mathbf{I}_\alpha\right\}\cdot\mathbf{T}. $$

Small molecule hyperfine structure
A typical simple example of the hyperfine structure due to the interactions discussed above is in the rotational transitions of hydrogen cyanide (1H12C14N) in its ground vibrational state. Here, the electric quadrupole interaction is due to the 14N-nucleus, the hyperfine nuclear spin-spin splitting is from the magnetic coupling between nitrogen, 14N (IN = 1), and hydrogen, 1H (IH = $1/2$), and a hydrogen spin-rotation interaction due to the 1H-nucleus. These contributing interactions to the hyperfine structure in the molecule are listed here in descending order of influence. Sub-doppler techniques have been used to discern the hyperfine structure in HCN rotational transitions.

The dipole selection rules for HCN hyperfine structure transitions are $$\Delta J = 1$$, $$\Delta F = \{0, \pm 1\}$$, where $J$ is the rotational quantum number and $F$ is the total rotational quantum number inclusive of nuclear spin ($$F = J + I_\text{N}$$), respectively. The lowest transition ($$J = 1 \rightarrow 0$$) splits into a hyperfine triplet. Using the selection rules, the hyperfine pattern of $$J = 2 \rightarrow 1$$ transition and higher dipole transitions is in the form of a hyperfine sextet. However, one of these components ($$\Delta F = -1$$) carries only 0.6% of the rotational transition intensity in the case of $$J = 2 \rightarrow 1$$. This contribution drops for increasing J. So, from $$J = 2 \rightarrow 1$$ upwards the hyperfine pattern consists of three very closely spaced stronger hyperfine components ($$\Delta J = 1$$, $$\Delta F = 1$$) together with two widely spaced components; one on the low frequency side and one on the high frequency side relative to the central hyperfine triplet. Each of these outliers carry ~$$\tfrac{1}{2} J^2$$ ($J$ is the upper rotational quantum number of the allowed dipole transition) the intensity of the entire transition. For consecutively higher-$J$ transitions, there are small but significant changes in the relative intensities and positions of each individual hyperfine component.

Measurements
Hyperfine interactions can be measured, among other ways, in atomic and molecular spectra and in electron paramagnetic resonance spectra of free radicals and transition-metal ions.

Astrophysics
As the hyperfine splitting is very small, the transition frequencies are usually not located in the optical, but are in the range of radio- or microwave (also called sub-millimeter) frequencies.

Hyperfine structure gives the 21 cm line observed in H I regions in interstellar medium.

Carl Sagan and Frank Drake considered the hyperfine transition of hydrogen to be a sufficiently universal phenomenon so as to be used as a base unit of time and length on the Pioneer plaque and later Voyager Golden Record.

In submillimeter astronomy, heterodyne receivers are widely used in detecting electromagnetic signals from celestial objects such as star-forming core or young stellar objects. The separations among neighboring components in a hyperfine spectrum of an observed rotational transition are usually small enough to fit within the receiver's IF band. Since the optical depth varies with frequency, strength ratios among the hyperfine components differ from that of their intrinsic (or optically thin) intensities (these are so-called hyperfine anomalies, often observed in the rotational transitions of HCN ). Thus, a more accurate determination of the optical depth is possible. From this we can derive the object's physical parameters.

Nuclear spectroscopy
In nuclear spectroscopy methods, the nucleus is used to probe the local structure in materials. The methods mainly base on hyperfine interactions with the surrounding atoms and ions. Important methods are nuclear magnetic resonance, Mössbauer spectroscopy, and perturbed angular correlation.

Nuclear technology
The atomic vapor laser isotope separation (AVLIS) process uses the hyperfine splitting between optical transitions in uranium-235 and uranium-238 to selectively photo-ionize only the uranium-235 atoms and then separate the ionized particles from the non-ionized ones. Precisely tuned dye lasers are used as the sources of the necessary exact wavelength radiation.

Use in defining the SI second and meter
The hyperfine structure transition can be used to make a microwave notch filter with very high stability, repeatability and Q factor, which can thus be used as a basis for very precise atomic clocks. The term transition frequency denotes the frequency of radiation corresponding to the transition between the two hyperfine levels of the atom, and is equal to $f = ΔE/h$, where $ΔE$ is difference in energy between the levels and $h$ is the Planck constant. Typically, the transition frequency of a particular isotope of caesium or rubidium atoms is used as a basis for these clocks.

Due to the accuracy of hyperfine structure transition-based atomic clocks, they are now used as the basis for the definition of the second. One second is now defined to be exactly $9,192,631,770$ cycles of the hyperfine structure transition frequency of caesium-133 atoms.

On October 21, 1983, the 17th CGPM defined the meter as the length of the path travelled by light in a vacuum during a time interval of $1⁄299,792,458$ of a second.

Precision tests of quantum electrodynamics
The hyperfine splitting in hydrogen and in muonium have been used to measure the value of the fine-structure constant α. Comparison with measurements of α in other physical systems provides a stringent test of QED.

Qubit in ion-trap quantum computing
The hyperfine states of a trapped ion are commonly used for storing qubits in ion-trap quantum computing. They have the advantage of having very long lifetimes, experimentally exceeding ~10 minutes (compared to ~1s for metastable electronic levels).

The frequency associated with the states' energy separation is in the microwave region, making it possible to drive hyperfine transitions using microwave radiation. However, at present no emitter is available that can be focused to address a particular ion from a sequence. Instead, a pair of laser pulses can be used to drive the transition, by having their frequency difference (detuning) equal to the required transition's frequency. This is essentially a stimulated Raman transition. In addition, near-field gradients have been exploited to individually address two ions separated by approximately 4.3 micrometers directly with microwave radiation.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Hyperfine structure


text:
Tribal name

A tribal name is a name of an ethnic tribe —usually of ancient origin, which represented its self-identity.

Studies of Native American tribal names show that most had an original meaning comparable to "human," "people" "us"—the "tribal" name for itself was often the localized ethnic self-perception of the general word for "human being."

In Israel, tribal names are used by the central election committee instead of town names, in cases where tribes do not live in recognized towns, or are nomadic.

title: Tribal name


text:
Talk:Bokelji

Not a separate ethnic group
Bokelji is a regional designation for inhabitants of Boka Kotorska, traditionally Croats and Serbs. It's really presumptuous to consider them a separate ethnic group, I've never heard of anyone claiming that before... --Shallot 23:09, 14 Mar 2004 (UTC)

And again, this is a pretty large leap with little basis in reality... they don't register on the census as Bokeljs, and from what I can see those are generally what everyone else refers to as the Croats from Boka. Incidentally, my grandfather was Ante Kosić and he said that his (Croatian) ancestors migrated from Krivošije (one of the hills overlooking Boka) about four centuries ago. I've always thought it was mildly amusing that my die-hard communist grandfather was possibly related to Ozana of Kotor, a blessed Catholic... :) --Shallot 00:54, 15 Mar 2004 (UTC)

 * The Krivošije are not only hills but a Serb Hercegovinian tribe that traces its original ancestors from Kosovo (the Samardžić family). They have remained Orthodox to this day, only a few migrants might have converted to Catholicism like your ancestors. Ozana of Kotor (Kata Kosić) on the other hand was not from the Krivošije but from Komani in Katunska nahija, Old Montenegro. She also converted to Catholicism when she moved to Kotor to served the Buci family and later became a Benedictine nun. --Igor 21:44, 16 Mar 2004 (UTC)

 * Ah, yes, we're all Serbs. I almost believed otherwise for a moment there! :P --Shallot 11:37, 17 Mar 2004 (UTC)

 * No, but the Krivošije are. As usual, you can check up on whatever it is that I am saying to you and as usual you will see that I am right as I was for Bosnia, Dubrovnik, Boskovic etc. --Igor 23:34, 19 Mar 2004 (UTC)

 * Oh, we've seen this tactic of yours before: throw in a few fairly inconsequent factoids and then spin whole article in a fairly ludicrous direction. --Shallot 11:33, 20 Mar 2004 (UTC)

 * Usually it takes time for you to, albeit silently, acknowledge my being right. I did not expect this time to be any different. If you are interested in drawing up your family's origins I would be glad to be of assistance. --Igor 21:54, 20 Mar 2004 (UTC)

 * Except that I'm not saying that you are right, neither silently nor verbally? You're merely hell-bent on making blatant logical fallacies (even in the unlikely case that what you said is completely true, and in the unlikely case that it applies directly to the family that I descended from, that still doesn't have to mean much with regards to the ethnic identification of those people, their direct progenies, and their descendents several centuries later).

 * I like your style, in the unlikely event that what I said is true :). As I said, check for yourself. Besides, you are the one who brought up personal details as an argument, not blame me for trying to correct you when it comes to facts. Fact is, you don't even know where the Krivošije are, let alone that you should ever had visited them, otherwise neither you nor Mir Harven would be writing this BS about Bokelji being Croat Catholics. I am the one that should give up on you but then again you would proclaim victory and continue writing your nonsense. --Igor 20:54, 26 Mar 2004 (UTC)

 * Making your opinion sound like universal fact must be fun, but it's also irrational when the opinion is biased. Anyway, I don't see why I'm still trying to argue against a propaganda tactic like that... --Shallot 16:44, 21 Mar 2004 (UTC)

The anti-Croatian stuff
I see Igor and the 24.* user had a field day with the page in the meantime. It is quite indicative that the number of Croats among these people is consistently downplayed, that their Catholic faith back from early medieval times is speciously denied, and that the historic values that they have preserved in their sacral objects is conveniently shoved under the rug. I mean, okay, there are possibly some ambiguities with assigning them modern ethnic identities, but the recent changes are just plain old biased towards Igor's good old pan-Serbian propaganda. --Shallot 20:22, 18 Mar 2004 (UTC)

 * Where did you get the information that Croats made up 50% of the population, according to which census?

 * First of all I never said that Croats made up 50% of "the population", because total population these days is clearly different.

 * Sorry, that's Mir Harven's. Consider it gone. --Igor 21:54, 20 Mar 2004 (UTC)

 * With reference to history, it's pointless to talk about censa when this whole article is really about a regional group rather than a nationality -- the latest census in Montenegro doesn't even mention Bokelji.

 * Your call, I can go either way, with or without censa figures, I just like sticking to the facts, no BS. --Igor 21:54, 20 Mar 2004 (UTC)

 * There's only a group referred to as "regional designation" but their numbers are comparable to the smaller minorities (since the war, the Croats are a good example of that), and the rest are Montenegrins and Serbs.

 * And not all of those (but certainly most) from the "regional designation" declared themselves as Bokelji. --Igor 21:54, 20 Mar 2004 (UTC)

 * Given that "Montenegrin" can also be a regional designation, and the experience from the Bunjevci case, I don't have much reason to believe that this designation isn't skewed either. --Shallot 11:33, 20 Mar 2004 (UTC)

 * Skewed, how so? ::: Your call, I can go either way, with or without censa figures, I just like sticking to the facts, no BS. --Igor 21:54, 20 Mar 2004 (UTC)

 * Skewed as in interpreted to mean one thing, when in reality it's something completely different. --Shallot 16:44, 21 Mar 2004 (UTC)

 * I am fully aware of the definition of skewed, was just hoping that you would, for once, support your baseless accusations against me. As usual, you are all talk. --Igor 20:54, 26 Mar 2004 (UTC)

 * Could you provide any information about the populace's alleged Croatdom prior to the 19th century?

 * "Alleged Croatdom", heh. I'd like to hear your explanation about how exactly the medieval southern Dalmatian/Illyrian duchies were Serbian, and only Serbian. I bet it's fun. --Shallot 11:33, 20 Mar 2004 (UTC)

 * You did not answer my question ... what else is new :). Duchies of Narentani/Pagania (Neretljani/Paganija), Terbounia(Travunija)-Konavli, Zahumlje are explicitely mentioned as being settled by Serbs in Porphyrogenitus's De_Administrando_Imperio and countless other Byzantine and even Roman sources say so. I'll write up a page on it just for you. --Igor 21:54, 20 Mar 2004 (UTC)

 * They're also referred to as Red Croatian duchies in that same work (in a different section, one that you oh-so-conveniently failed to reproduce in the Wikipedia article), and elsewhere. --Shallot 16:44, 21 Mar 2004 (UTC)

 * Which section? :) This is a trick question, there is no such section. Shallot, get your facts straight, then come back to argue. --Igor 20:54, 26 Mar 2004 (UTC)

 * A quick google search provided me with the footnotes section of "Croats & Serbs", book by one Dominik Mandic. First footnote mentioning the emperor is number 14,

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Reaction to the article "Croatized Bulgars"?????!?!?!!?!!?!
Whoever wrote this has no clue about Serbian history whatsoever!!!!!!!!! Serbs as a nation first appeared in articles of Claudius Ptolomy, Tacitus and Plinius in 1st-2nd centuries A.D. When they were invited to the Balkans by Heraclius, they settled along with Croats, who were another tribal nation at that time. BULGARS originate from Pamir and Turkic people of Asia and have moved to the Balkans about 50 years after it got colonized by Serbs and Croats; Bulgar tribes mixed with those Slavic peoples and became Bulgarians (Slavic speakers) but not until 9th century! Croats and Serbs have had their own tribal leaders who would later become zupans and kings of their respective nations. They did not mix a lot during the time as they were considered separate nations (like Flems and Dutch today). Same thing with the Bulgarians; even when Serbia was briefly held by Bularians Serbs have had their own kings and dynasties, so Serbia was never part of Bulgaria but more as an semi-independent or vassal state. Bulgarian language could be inteligible with Serbian but also has many differences since it was heavily influenced by Thracian, Dacian and Greek language, later also by Turkish and very much Russian. Serbian language is based on 2 dialects: ekavica and ijekavica, not just ekavica! Over 30% of all Serbs speak ijekavica, mostly in the West (Bosnia, Croatia, MOntenegro but also parts of Western Serbia and Sandzak). That is the result of the same literary school that was accepted in both Bulgaria and Serbia (Ohrid), but that's where all similarities end. Serbian and Croatian are still linguistically one language as they have always been (like Flemish and Dutch), and BUlgarian has ALWAYS been a separate language since it is not as well understood by other South Slavs (except Macedonians). So you could say that Serbs gave a large contribution to converting Bulgars into Slavic, not vice versa (since the Bulgarians settled the areas previously held by Serb tribes down to Salonica and Constantinople)! Even though Boche di Cattaro (Boka Kotorska) was under strong Catholic influence throughout most of the 2nd millenia, this does not mean that it hasn't been Serbian at the same time! It's quite the opposite actually, taking that majority of the population in that area today are Orthodox Serbs (f.e. Herceg Novi- king Tvrtko's city, one of the pearls of Serbian culture). You have to take into account that Dioclea and later Zeta were the heart of Serbian State, which was at that time religiously split; Mihajlo Bodin of Zeta might have ackgnowledged supremacy of the Pope to obtain the title of King of Dioclea, but he's considered to be one of the fathers of Serbian nation, even though he owed alligeance to the West. Stefan Nemanja, first Great Zupan, was a Catholic by birth like most of "Diocleans" but he's considered to be the greatest Serb of all times (together with other members of his own dynasty). Even today many Catholics in Bay of Kotor consider themselves to be Serbs. Citizens of this area proclaimed unification with Serbia independetly from the rest of the Western Lands after WWI.Boka managed to preserve its Orthodox caracter despite cultural assimilation due to its indented position (inland bay) and closness of Serb nation present in Herzegovina on the West and Hills in the East. "Orthodox christian presence in Boka is so obviously shallow and recent, it was visible even to my, tourist's, naked eye. What an disappointment it was, after imagining all this years that there ever was such a thing as Serb naval tradition".- Tell me, who has built Herceg Novi? Orthodox King Tvrtko, in the 15th century. Who has built the temple "Our Lady of Rocks"? Catholic Serb families from Perast. If you actually went there they would tell you the same thing. Let me remind you that at one time (Czar Dushan) Serbian Empire had outlets on 3 sees, practically controlling the entire trade on Central Mediterranean. Emperor of Byzantium Jovan Kantakuzin has critized his rival Dushan for "trading with the West" (Venice, Genoa etc), which was at that time considered immoral. He has besieged Constantinople in numerous occasions with his navy- however he never succedeed in conquering the city (maybe it was lack of naval experience), but Serbia has been a Mediterranean state throughout most of its history! Had it nor been, it wouldn'y have had an outlet to the sea at all (if she could not defend it with its navy). User:NeroN_BG

??
"There was no explicit expression of Serbian ethnic consciousness among Catholic Montenegrins (as Dioclea, then Zeta became known), particularly in the large tribes of Bjelopavlovići, Piperi or Bratnožići"- this is a ridicilous claim taking that those clans were formed as late as the Ottoman period! King of Dioclea Michael Bodin was a ruler of the Serbs and so were his successors; Nemanjic dynasty originates from today's Podgorica and was of a Serbian Catholic origin. The term "Montenegrins" did not exist prior to the 15th century and was a local delimination just as the Bokelji, Krajishnici etc. You realize how stupid that sentence is taking that Montenegrins did not exist in form of a distinct nationality before Tito (check Demographic history of Montenegro). Up until WWII citizens of Montenegro have overwhelmingly opted for Serbian origin (the number would always surpass 90%). The Censuses have first been conducted since 1855 and none of them (up until 1948) have recorded a Montenegrin nationality, which is quite strange taking that until 1918 Montenegro was a separate state. However this state governed by King Nikola defined itself as the purest of all Serb states and aspired to be the leader of the "Second Serbian Empire". User:NeroN_BG

Article plagiarized?
I see some people want to rewrite this article. That's good. However, you must first deal with the fact that the last two sections of the article have basically been copy and pasted from. I say "basically" because the term 'Croat' has been deleted and replaced by 'Bokelj' in every case. This info may be a copyright infringment (I'm not sure, the website allows some free usage), but it certainly does not speak of Bokelji, rather Croatians from Boka which this article completely distorts. --Thewanderer 17:53, 23 September 2006 (UTC)

 * Wanderer, yeah, could you help over 'ere. I think we've made a mess of the article. --PaxEquilibrium 11:31, 12 January 2007 (UTC)

 * Well I'm all in favour of acceptance. I believe that they may have previously called themselves Croats, but proper statistics are hard to find. Censa indicate percentage of people with regard ethnicity, language, religion etc. according to region. When you count the number of Croats in Montenegro, it is hard to prove that the people who declared the name are or are not from the Bokeljs. If we can, then this article can be based on a community who identify as Bokeljs at a regional level like the Romania-based Krashovans do when they mostly identify as Croats at the national level. Equally, if most are insistent on calling themselves Bokeljs by ethnicity then we cannot assert that they are either Serb, Croat or Montenegrin. We can say that they are Slavic in that this is an ethnicity of an ethnicity itself, and if it can be proved, we can say that they previously declared themselves Croats (or whatever else). What is dangerous however is to return to the old disputes that they can call themselves as they choose, they are still Serbs, or still Croats etc as if to suggest that there is something concrete about being Serb or Croat when there simply isn't that. And the other thing is that if they are nationally identifying as Bokeljs on one census in contrast to a previous edition, there is every possibility that some if only few who took the name may have been Serbs or Montenegrins. Nationality moves in mysterious ways. Evlekis 18:02, 12 January 2007 (UTC)

POV
I haven't seen more biased article in a long while. According to people who have never even seen Boka, Bokelji were and are Serbs, we are all loyal to the Serbian Orthodox Church, Budva is a part of Boka(which is, you must agree, contradictory to the common sense), and celebrating "slava" makes us Serbs, because no one in the whole world has patron saints but Serbs... Thus, I added the POV tag.Didn't have time to revise the page, but something has to be done asap. Sideshow Bob 23:14, 17 January 2007 (UTC)

 * Well, Bokelji were and are Serbs, the Montenegrin Orthodox Church is little or none at all active in the Bay (which is the HQ of the Serbian Orthodox Church's activity and the Serbian institutions in Montenegro). Budva indeed is historically a part of Boka, and as a the Gulf is considered to be more of a historical entity, its residents still consider it (although it aint geographically, of course). --PaxEquilibrium 23:36, 17 January 2007 (UTC)

title: Talk:Bokelji


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List of prime ministers of Spain

The prime minister of Spain is the head of government of Spain. There is no specific date as to when the office of Prime Minister first appeared as the role was not created, but rather evolved over a period of time through a merger of duties. Modern historians have not managed to agree who the first prime minister of Spain was, but Francisco Martínez de la Rosa was the first prime minister recognized by a constitutional law (the Spanish Royal Statute of 1834).

In contemporary Spain, the first Prime Minister of the Kingdom of Spain since the approval of the Constitution was Adolfo Suárez. Due to the gradual evolution of the post, the title has been applied to early prime ministers retroactively. The following list therefore includes those who have been referred to as various other titles since the creation of the Council of Ministers in 1823.

Since the reign of Philip V, prime ministers have received several names, such as First Secretary of State (until 1834), President of the Council of Ministers (1834–1868; 1874–1923; 1925–1939), President of the Executive Power (1874) or President of the Government (1973–present), among others. Between 1938 and 1973, the post of President of the Government was personally linked to the person serving as Head of State.

Before 1823
There is no specific date when the office of prime minister first appeared as the role was not created, but rather evolved over a period of time through merger of duties. The government was led by a Valido, a favourite of the Monarch or the ruling Regent. Since 1621, there was also a Secretary of State of the Universal Bureau (Secretario de Estado y del Despacho Universal), but this seems to have been rather a subordinate position.

Later, the reforms introduced by Phillip V in the 1710s established several secretaries of state for specific government areas, and the secretary of State for Foreign Affairs (Secretario de Estado y del Despacho de Estado) was eventually known as the First Secretary of State due to its de facto role as primer minister. This position was consolidated with the establishment of the Council of Ministers in 1823 which the First Secretary of State chaired over in the king's absence, and in 1834 the First Secretary of State became known as President of the Council of Ministers.

John II (1406–1454)

 * Álvaro de Luna

Henry IV (1454–1474)

 * Juan Pacheco
 * Beltrán de la Cueva
 * Miguel Lucas de Iranzo

Philip III (1598–1621)

 * Francisco de Sandoval y Rojas (1598–1618)
 * Cristóbal Gómez de Sandoval y de la Cerda (1619–1621)

Philip IV (1621–1665)

 * Baltasar de Zúñiga (1621–1622)
 * Gaspar de Guzmán, Count-Duke of Olivares (1622–1643)
 * Luis de Haro (1643–1661)

Charles II (1665–1700)

 * Juan Everardo Nithard (1666–1669)
 * Fernando de Valenzuela (1671–1676)
 * Juan José de Austria (1677–1679)
 * Duke of Medinaceli (1679–1685)
 * Count of Oropesa (1685–1699)
 * Luis Manuel Fernández de Portocarrero (1699–1703)

Office title

 * First Secretary of State (1823–1834)
 * President of the Council of Ministers (1834–1868; 1869–1873; 1874–1923; 1925–1931; 1931–1939)
 * President of the Provisional Government and of the Council of Ministers (1868–1869)
 * President of the Executive Power (1869; 1873–1874)
 * Head of the Government and President of the Military Directory (1923–1925)
 * President of the Provisional Government (1931)
 * Head of State and President of the Government (1938–1973)
 * President of the Government (1973–present)

Kingdom of Spain (1823–1868)
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Democratic Sexennium and First Republic (1868–1874)
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Bourbon Restoration in Spain (1874–1931)
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Second Spanish Republic (1931–1939)
Governments: •

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Francoist Spain (1936–1975)
Governments:

Kingdom of Spain (1975–present)
Governments:

title: List of prime ministers of Spain


text:
Goren (surname)

Goren is a surname. Notable people with the surname include:

 * Ali Ferit Gören (1913-1987), Austrian-Turkish Olympic sprinter
 * Arthur A. Goren, scholar and professor of American Jewish history
 * Charles Goren, American bridge player, writer, and advocate
 * Lee Goren, Canadian hockey player
 * Or Goren (born 1956), Israeli basketball player
 * Shlomo Goren, former Ashkenazi Chief Rabbi of Israel
 * Ran Goren, Israeli fighter pilot and Major General of the IDF

Fictional characters

 * Robert Goren, a character in the television series Law & Order: Criminal Intent

title: Goren (surname)


text:
RFA Bayleaf (A79)

RFA Bayleaf (A79) was a Leaf-class support tanker of the Royal Fleet Auxiliary, and the second ship to bear the name.

Bayleaf was launched by the Furness Shipbuilding Company of Stockton-on-Tees. She was launched as the civilian London Integrity for London & Overseas Freighters in 1954 and completed in 1955. She was a sister ship of RFA Brambleleaf (A81) built by the same shipyard for LOF the previous year.

She was bareboat chartered for the RFA in 1959 and renamed RFA Bayleaf. She was returned to her owners in 1973, with whom she traded as the London Integrity again until the end of 1976.

On 7 January 1977 she was sold for scrap and on 25 January 1977 she arrived in Burriana in Spain to be broken up.

title: RFA Bayleaf (A79)


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RFA Brambleleaf (A81)

RFA Brambleleaf (A81) was a Leaf-class tanker support tanker of the Royal Fleet Auxiliary (RFA), the naval auxiliary fleet of the United Kingdom. Originally built as MV Hudson Deep she was chartered by the Ministry of Defence (MoD) in 1980.

Operational history
In April 1982, Brambleleaf was diverted from Armilla patrol duties in the Persian Gulf for service during the Falklands Conflict. Due to damage sustained due to severe weather, Brambleleaf transferred her cargo to RFAUX Tidespring (A75) off South Georgia and returned to the UK for repairs during May prior to returning to the South Atlantic in June, and again in August.

On 18 November 1983, Brambleleaf sailed along with the assault ship HMS Fearless to support Operation Offcut, providing naval support for British troops in the multi-national force in Lebanon.

In 2003, Brambleleaf was one of 13 RFA ships deployed in support of the second Gulf War.

On 18 August 2009 she was towed to Ghent for scrapping.

title: RFA Brambleleaf (A81)


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Walter Stanley Monroe

Walter Stanley Monroe (May 14, 1871 – October 6, 1952) was a businessman and conservative politician who served as Prime Minister of Newfoundland from 1924 to 1928 as leader of the Liberal-Conservative Progressive Party.

He was born in Ireland in 1871, the first son of John Monroe, a distinguished lawyer who became Solicitor-General for Ireland, and his wife Elizabeth Moule. He was educated at the Harrow School, England. He emigrated to Newfoundland to join his uncle, Moses Monroe, at the age of 17 in 1888.

Monroe was a successful businessman who briefly served in the government of William Warren. He emerged from the political crisis that destroyed the governments of Sir Richard Squires and William Warren as leader of a new party, the Liberal-Conservative Progressive Party, which had been cobbled together by Warren and the opposition Conservatives after Warren's government fell. The party was essentially a conservative party and swept to power in the 1924 election, weeks after it was formed.

The Monroe government saw a successful settlement of the Labrador boundary dispute with Canada after Newfoundland successfully argued its case at the Judicial Committee of the Privy Council in London. As Prime Minister, one of his first moves in power was to abolish the personal income tax, and to reduce corporate taxes paid by banks. His government introduced a franchise bill to the legislature in 1925, where it passed unanimously on March 9, and became law on April 13, 1925. Now, women were allowed to vote in elections for the first time. Monroe returned to private life and resigned on August 15, 1928 passing the leadership of the party to his cousin Frederick C. Alderdice who became the new Prime Minister. In 1929, Mr. Monroe was made a member of the Legislative Council of Newfoundland.

title: Walter Stanley Monroe


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RFA Cherryleaf (A82)

RFA Cherryleaf (A82) was a Leaf-class small fleet tanker of the Royal Fleet Auxiliary (RFA), the naval auxiliary fleet of the United Kingdom, in service from 1973 to 1980.

History
She was built by Nordseewerke in Emden, Germany and launched in 1962 as Overseas Adventurer for London and Overseas Bulk Carriers, a subsidiary of London & Overseas Freighters (LOF). She was bareboat chartered for the RFA in February 1973 and renamed RFA Cherryleaf.

In 1980 she was returned to LOF and her name reverted to Overseas Adventurer. In 1981 LOF sold her to Petrostar Co Ltd of Saudi Arabia who renamed her Petrostar XVI.

On 5 April 1986 during the Tanker War phase of the Iran–Iraq War she was off Halul Island en route from Bahrain to Sharjah when Iranian helicopters hit her with AGM-65 Maverick missiles. Her accommodation was gutted by fire and four crewmembers were killed. She was towed to Sharjah where she was declared a constructive total loss on 9 April 1986 and laid up for disposal. She was sold to National Ship Demolition Co Ltd of Taiwan, arrived Kaohsiung on 24 January 1987 and her demolition began on 19 February 1987.

title: RFA Cherryleaf (A82)


text:
User talk:Voivod~enwiki

Dude, I figured it was only a matter of time before you showed up here! I have so much stuff to tell you about, but I lost your number when you moved and I'm so lazy I never bothered to track it down on the 'net. Maury 23:12, 14 Mar 2004 (UTC)

Your account will be renamed
Hello,

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Unfortunately, your account clashes with another account also called Voivod. To make sure that both of you can use all Wikimedia projects in future, we have reserved the name Voivod~enwiki that only you will have. If you like it, you don't have to do anything. If you do not like it, you can pick out a different name. If you think you might own all of the accounts with this name and this message is in error, please visit Special:MergeAccount to check and attach all of your accounts to prevent them from being renamed.

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Renamed
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title: User talk:Voivod~enwiki


text:
RFA Appleleaf (A83)

RFA Appleleaf (A83) was a Leaf-class tanker of the Royal Fleet Auxiliary in service between 1959 and 1970.

title: RFA Appleleaf (A83)


text:
RFA Olwen (A122)

RFA Olwen (A122) was an Ol-class "fast fleet tanker" of the Royal Fleet Auxiliary (RFA), the naval auxiliary fleet of the United Kingdom. She was the lead ship of her class, and launched in 1964 as RFA Olynthus, the second ship to bear this name. She was renamed Olwen in 1967 to avoid confusion with the Oberon-class submarine, HMS Olympus.

1970
In November and December 1970 Olwen was involved in Operation Burlap giving humanitarian assistance to East Pakistan after a cyclone caused extensive damage and flooding.

1973
In the Second Cod War, Olwen supported Royal Navy ships three times.

Decommissioning
She was decommissioned in 1999 and laid up at Portsmouth, before being broken up at Alang, India in 2001.

title: RFA Olwen (A122)


text:
RFA Olna (A123)

RFA Olna (A123) was the third and final of the three Ol-class "fast fleet tanker" of the Royal Fleet Auxiliary. Olna saw service in the Falklands War.

Background
Her design was a development of the Tide-class ships of the late 1950s. She was commissioned in 1966 and served in the RFA for 34 years. Olna was the third ship of the Royal Fleet Auxiliary to bear the name.

Operational history
Olna entered service as the UK was pulling back from its final large imperial garrisons. Much of the ship's early life was spent supporting routine deployments around the world.

1967-1968
In Operation Magister, Olna was part of the fleet covering the final British military withdrawal from Aden, along with nine other RFAs.

Falklands War
In 1982 Olna left for the South Atlantic as part of the second wave of ships to leave the UK during the Falklands War. That group was centred on the destroyer HMS Bristol. Once Olna reached theatre, her time was primarily spent fuelling the carrier battle group.

1983-2000
In 1990, another wartime deployment beckoned. As forces built up in the Persian Gulf, Olna joined the British task force on station. Olna arrived in August 1990, shortly after Iraq invaded Kuwait, and apart from a short maintenance period in Singapore was on station for the whole duration of the conflict. Olna operated further north than any other tanker as the US Navy was wary of mines after two ships had been severely damaged.

At the end of the 1990s, retirement was in sight. 1999 and 2000 were spent in mothballs at Gibraltar until the outbreak of a crisis in Sierra Leone called for Olna to make one last deployment. The ship did not proceed to Sierra Leone, but instead relieved other RFA vessels of participation in a major exercise off Scotland. Following this exercise, the ship returned to reserve and decommissioned soon thereafter.

Decommissioning
In March 2001, Olna was sold to a Turkish shipbreaking firm, but owing to the high quantity of asbestos aboard she was diverted to Greece before finally going to Indian breakers.

title: RFA Olna (A123)