||This article needs additional citations for verification. (August 2007)|
A fighter aircraft is a military aircraft designed primarily for air-to-air combat against other aircraft, as opposed to bombers and attack aircraft, whose main mission is to attack ground targets. The hallmarks of a fighter are its speed, maneuverability, and small size relative to other combat aircraft.
Many fighters have secondary ground-attack capabilities, and some are designed as dual-purpose fighter-bombers. Often, aircraft that do not fulfill the standard definition are called fighters. This may be for political or national security reasons, or for advertising purposes or other reasons.
A fighter's main purpose is to establish air superiority over a battlefield. Since World War I, achieving and maintaining air superiority has been considered essential for victory in conventional warfare. The success or failure of a belligerent's efforts to gain air supremacy hinges on several factors including the skill of its pilots, the tactical soundness of its doctrine for deploying its fighters, and the numbers and performance of those fighters. Because of the importance of air superiority, since the dawn of aerial combat armed forces have constantly competed to develop technologically superior fighters and to deploy these fighters in greater numbers, and fielding a viable fighter fleet consumes a substantial proportion of the defense budgets of modern armed forces.
The word "fighter" did not become the official English term for such aircraft until after World War I. In Great Britain's Royal Flying Corps and Royal Air Force these aircraft were referred to as "scouts" into the early 1920s. The U.S. Army called their fighters "pursuit" aircraft from 1916 until the late 1940s. The French chasseur and German Jagdflugzeuge are terms that continue to be used for fighters, and mean "hunter" and "hunting aircraft" respectively. Most languages follow this, except Russian where the fighter is an "истребитель" (pronounced "istrebitel"), meaning "exterminator", and Hebrew where it is "matose krav" (literally "battle plane").
As a part of military nomenclature, a letter is often assigned to various types of aircraft to indicate their use, along with a number to indicate the specific aircraft. The letters used to designate a fighter differ in various countries — in the English speaking world, "F" is now used to indicate a fighter (e.g. F-35 or Spitfire F.22), though when the pursuit designation was used in the US, they were "P" types (e.g. P-40). In Russia "I" was used (I-16), while the French continue to use "C" (Nieuport 17 C.1).
Although the term "fighter" specifies aircraft designed to shoot down other aircraft, such designs are often also useful as multirole fighter-bombers, strike fighters, and sometimes lighter, fighter-sized tactical ground-attack aircraft. This has always been the case, for instance the Sopwith Camel and other "fighting scouts" of World War I performed a great deal of ground-attack work. In World War II, the USAAF and RAF often favored fighters over dedicated light bombers or dive bombers, and types such as the P-47 Thunderbolt and Hawker Hurricane that were no longer competitive fighters were relegated to ground attack. A number of aircraft, such as the F-111 and F-117, had no fighter capability despite carrying the designation but did so for political reasons. The F-111 was originally intended for a fighter role with the Navy, but this variant was cancelled. This blurring follows the use of fighters from their earliest days for "attack" or "strike" operations against enemy troops, field positions, vehicles, and facilities by means of strafing or dropping small bombs and incendiaries. Versatile multirole fighter-bombers such as the F/A-18 Hornet are a less expensive option than having a range of specialized aircraft types.
Some of the most expensive fighters such as the F-14 Tomcat, F-22 Raptor and F-15 Eagle were employed as all-weather interceptors as well as air superiority fighter aircraft, while commonly developing air-to-ground roles late in their careers. An interceptor is generally an aircraft intended to target (or intercept) bombers and so often trades maneuverability for climb rate.
Development overview 
Fighters were developed in World War I to deny enemy aircraft and dirigibles the ability to gather information by reconnaissance. Early fighters were very small and lightly armed by later standards, and most were biplanes built with a wooden frame, covered with fabric, and limited to about 100 mph. As control of the airspace over armies became increasingly important all of the major powers developed fighters to support their military operations. Between the wars, wood was largely replaced by steel tubing, then aluminium tubing, and finally aluminium stressed skin structures began to predominate.
By World War II, most fighters were all-metal monoplanes armed with batteries of machine guns or cannons and some were capable of speeds approaching 400 mph. Most fighters up to this point had one engine, but a number of twin-engine fighters were built; however they were found to be outmatched against single-engine fighters and were relegated to other tasks, such as night fighters equipped with primitive radar sets.
By the end of the war, turbojet engines were replacing piston engines as the means of propulsion, further increasing aircraft speed. Since the weight of the engine was so much less than on piston engined fighters, having two engines was no longer a handicap and one or two were used, depending on requirements. This in turn required the development of ejection seats so the pilot could escape and G-suits to counter the much greater forces being applied to the pilot during maneuvers.
In the 1950s, radar was fitted to day fighters, since pilots could no longer see far enough ahead to prepare for any opposition. Since then, radar capabilities have grown enormously and are now the primary method of target acquisition. Wings were made thinner and swept back to reduce trans-sonic drag, which required new manufacturing methods to obtain sufficient strength. Skins were no longer sheet metal rivetted to a structure, but milled from large slabs of alloy. The sound barrier was broken, and after a few false starts due to required changes in controls, speeds quickly reached Mach 2—past which aircraft can't maneuver to avoid attack.
Air-to-air missiles largely replaced guns and rockets in the early 1960s since both were believed unusable at the speeds being attained, however the Vietnam War showed that guns still had a role to play and most fighters built since then are fitted with cannon (typically between 20 and 30 mm in caliber) as an adjunct to missiles. Most modern combat aircraft can carry a pair of basic air-to-air missiles and some of the larger fighters such as the Sukhoi Su-27 can carry as many as 12.
In the 1970s, turbofans replaced turbojets, improving fuel economy sufficiently that the last piston engined support aircraft could be replaced with jets, making multi-role combat aircraft possible. Honeycomb structures began to replace milled structures, and the first composite components began to appear on components subjected to little stress.
With the steady improvements in computers, defensive systems have become increasingly efficient and to counter this, stealth technologies have been pursued by the United States, Russia, India and China. The first step in this was to find ways to reduce the aircraft's reflectivity to radar waves by burying the engines, eliminating sharp corners and diverting any reflections away from the radar sets of opposing forces. Various materials were found to absorb the energy from radar waves, and were incorporated into special finishes that have since found widespread application. Composite structures have become widespread, and include major structural components, and have helped to counterbalance the steady increases in aircraft weight—most modern fighters are larger and heavier than World War 2 medium bombers.
Piston engine fighters 
World War I 
The word "fighter" was first used to describe a two-seater aircraft with sufficient lift to carry a machine gun and its operator as well as the pilot. Some of the first such "fighters" belonged to the "gunbus" series of experimental gun carriers of the British Vickers company that culminated in the Vickers F.B.5 Gunbus of 1914. The main drawback of this type of aircraft was its lack of speed. Planners quickly realized that an aircraft intended to destroy its kind in the air had to be fast enough to catch its quarry.
Another type of military aircraft was to form the basis for an effective "fighter" in the modern sense of the word. It was based on the small fast aircraft developed before the war for such air races as the Gordon Bennett Cup and Schneider Trophy. The military scout airplane was not expected to carry serious armament, but rather to rely on its speed to reach the scout or reconnoiter location and return quickly to report—essentially an aerial horse. British scout aircraft, in this sense, included the Sopwith Tabloid and Bristol Scout. French equivalents included the Morane-Saulnier N.
Soon after the commencement of the war, pilots armed themselves with pistols, carbines, grenades, and an assortment of improvised weapons. Many of these proved ineffective as the pilot had to fly his airplane while attempting to aim a handheld weapon and make a difficult deflection shot. The first step in finding a real solution was to mount the weapon on the aircraft, but the propeller remained a problem since the best direction to shoot is straight ahead. Numerous solutions were tried. A second crew member behind the pilot could aim and fire a swivel-mounted machine gun at enemy airplanes however, this limited the area of coverage chiefly to the rear hemisphere, and effective coordination of the pilot's maneuvering with the gunner's aiming was difficult. This option was chiefly employed as a defensive measure on two-seater reconnaissance aircraft from 1915 on. Both the SPAD A.2 and the Royal Aircraft Factory B.E.9 added a second crewman ahead of the engine in a pod but this was both hazardous to the second crewman and limited performance. The Sopwith L.R.T.Tr. similarly added a pod on the top wing with no better luck.
An alternative was to build a "pusher" scout such as the Airco DH.2, with the propeller mounted behind the pilot. The main drawback was that the high drag of a pusher type's tail structure made it slower than a similar "tractor" aircraft.
A better solution for a single seat scout was to mount the machine gun (rifles and pistols having been dispensed with) to fire forwards but outside the propeller arc. Wing guns were tried but the unreliable weapons available required frequent clearing of jammed rounds and misfires and remained impractical until after the war. Mounting the machine gun over the top wing worked well and was used long after the ideal solution was found. The Nieuport 11 of 1916 and Royal Aircraft Factory S.E.5 of 1918 both used this system with considerable success, however this placement made aiming difficult and the location made it difficult for a pilot to both maneuver and have access to the gun's breech. The British Foster mounting was specifically designed for this kind of application, fitted with the Lewis Machine gun, which due to its design was unsuitable for synchronizing.
The need to arm a tractor scout with a forward-firing gun whose bullets passed through the propeller arc was evident even before the outbreak of war and inventors in both France and Germany devised mechanisms that could time the firing of the individual rounds to avoid hitting the propeller blades. Franz Schneider, a Swiss engineer, had patented such a device in Germany in 1913, but his original work was not followed up. French aircraft designer Raymond Saulnier patented a practical device in April 1914, but trials were unsuccessful because of the propensity of the machine gun employed to hang fire due to unreliable ammunition.
In December 1914, French aviator Roland Garros asked Saulnier to install his synchronization gear on Garros' Morane-Saulnier Type L. Unfortunately the gas-operated Hotchkiss machine gun he was provided had an erratic rate of fire and it was impossible to synchronize it with a spinning propeller. As an interim measure, the propeller blades were armored and fitted with metal wedges to protect the pilot from ricochets. Garros' modified monoplane was first flown in March 1915 and he began combat operations soon thereafter. Garros scored three victories in three weeks before he himself was downed on 18 April and his airplane, along with its synchronization gear and propeller was captured by the Germans.
Meanwhile, the synchronization gear (called the Stangensteuerung in German, for "pushrod control system") devised by the engineers of Anthony Fokker's firm was the first system to see production contracts, and would make the Fokker Eindecker monoplane a feared name over the Western Front, despite its being an adaptation of an obsolete pre-war French Morane-Saulnier racing airplane, with a mediocre performance and poor flight characteristics. The first victory for the Eindecker came on 1 July 1915, when Leutnant Kurt Wintgens, flying with the Feldflieger Abteilung 6 unit on the Western Front, forced down a Morane-Saulnier Type L two-seat "parasol" monoplane just east of Luneville. Wintgens' aircraft, one of the five Fokker M.5K/MG production prototype examples of the Eindecker, was armed with a synchronized, air-cooled aviation version of the Parabellum MG14 machine gun.
The success of the Eindecker kicked off a competitive cycle of improvement among the combatants, building ever more capable single-seat fighters. The Albatros D.I and Sopwith Pup of 1916 set the classic pattern followed by fighters for about twenty years. Most were biplanes and only rarely monoplanes or triplanes. The strong box structure of the biplane wing provided a rigid wing that allowed the accurate lateral control essential for dogfighting. They had a single operator, who flew the aircraft and also controlled its armament. They were armed with one or two Maxim or Vickers machine guns, which were easier to synchronize than other types, firing through the propeller arc. Gun breeches were directly in front of the pilot with obvious implications in case of accidents, but jams could be cleared in flight, while aiming was simplified.
The use of metal aircraft structures was pioneered before World War I by Breguet but would find its biggest proponent with Anthony Fokker who used chrome-molybdenum steel tubing for the fuselage structure of all his fighter designs, while the innovative German engineer Hugo Junkers developed two all-metal, single-seat fighter monoplane designs with cantilever wings: the strictly experimental Junkers J 2 private-venture aircraft, made with steel, and some forty examples of the Junkers D.I, made with corrugated duralumin, all based on his experience in creating the pioneering Junkers J 1 all-metal airframe technology demonstration aircraft of late 1915. While Fokker would pursue steel tube fuselages with wooden wings until the late 1930s, and Junkers would focus on corrugated sheet metal, Dornier was the first to build a fighter (The Dornier D.I) made with pre-stressed sheet aluminium and having cantelevered wings, a form that would replace all others in the 1930s.
As collective combat experience grew, the more successful pilots such as Oswald Boelcke, Max Immelmann, and Edward Mannock developed innovative tactical formations and maneuvers to enhance their air units' combat effectiveness.
Allied and—before 1918—German pilots of World War I were not equipped with parachutes, so in-flight fires or structural failure were often fatal. Parachutes were well-developed by 1918 having previously been used by balloonists, and were adopted by the German flying services during the course of that year (the famous "Red Baron" was wearing one when he was killed), but the allied command continued to oppose their use on various grounds.
In April 1917, during a brief period of German aerial supremacy, a grandstanding Member of Parliament (upset at the lack of orders for his own aircraft manufacturing firm) claimed that, on the Western Front, a British pilot's average life expectancy was 93 flying hours, or about three weeks of active service. More than 50,000 airmen from both sides died during the war.
Inter-war period (1919–38) 
Fighter development stagnated between the wars, especially in the United States and the United Kingdom, where budgets were small. In France, Italy and Russia, where large budgets continued to allow major development, both monoplanes and all metal structures were common by the end of the 1920s however those countries overspent themselves and were overtaken in the '30s by those powers that hadn't been spending heavily, namely the British, the Americans and the Germans.
Given limited defense budgets, air forces tended to be conservative in their aircraft purchases, and biplanes remained popular with pilots because of their agility, and remained in service long after they had ceased to be competitive. Designs such as the Gloster Gladiator, Fiat CR.42, and Polikarpov I-15 were common even in the late 1930s, and many were still in service as late as 1942. Up until the mid-1930s, the majority of fighters in the US, the UK, Italy and Russia remained fabric-covered biplanes.
Fighter armament eventually began to be mounted inside the wings, outside the arc of the propeller, though most designs retained two synchronized machine-guns directly ahead of the pilot where they were more accurate (that being the strongest part of the structure). Rifle-caliber .30 and .303 in (7.62 mm) caliber guns remained the norm with larger weapons either being too heavy and cumbersome or deemed unnecessary against such lightly built aircraft. It was not considered unreasonable to use World War I-style armament to counter enemy fighters as there was insufficient air to air combat during most of the period to disprove this notion.
The rotary engine, popular during World War I, quickly disappeared, having reached its peak as rotational forces prevented more fuel and air from being delivered to the cylinders, which limited horsepower. They were replaced chiefly by the stationary radial engine though major advances led to inline engines, which gained ground with several exceptional engines—including the 1,145 cu in (18.76 l) V-12 Curtiss D-12. Aircraft engines increased in power several-fold over the period, going from a typical 180 hp (130 kW) in the 1918 Fokker D.VII to 900 hp (670 kW) in the 1938 Curtiss P-36. The debate between the sleek in-line engines versus the more reliable radial models continued, with naval air forces preferring the radial engines, and land-based forces often choosing in-line units. Radial designs did not require a separate (and vulnerable) cooling system, but had increased drag. In-line engines often had a better power-to-weight ratio, but there were radial engines that kept working even after having suffered significant battle damage.
Some air forces experimented with "heavy fighters" (called "destroyers" by the Germans). These were larger, usually twin-engined aircraft, sometimes adaptations of light or medium bomber types. Such designs typically had greater internal fuel capacity (thus longer range) and heavier armament than their single-engine counterparts. In combat, they proved vulnerable to more agile single-engine fighters.
The primary driver of fighter innovation, right up to the period of rapid re-armament in the late 1930s, were not military budgets, but civilian aircraft racing. Aircraft designed for these races introduced innovations like streamlining and more powerful engines that would find their way into the fighters of World War II. The most significant of these was the Schneider Cup races, where competition grew so fierce, only national governments could afford to enter.
At the very end of the inter-war period in Europe came the Spanish Civil War. This was just the opportunity the German Luftwaffe, Italian Regia Aeronautica, and the Soviet Union's Red Air Force needed to test their latest aircraft. Each party sent numerous aircraft types to support their sides in the conflict. In the dogfights over Spain, the latest Messerschmitt Bf 109 fighters did well, as did the Soviet Polikarpov I-16. The German design had considerably more room for development however and the lessons learned led to greatly improved models in World War II. The Russians, whose side lost, failed to keep up and despite newer models coming into service, I-16s were outfought by the improved Bf 109s in World War II, while remaining the most common Soviet front-line fighter into 1942. For their part, the Italians developed several monoplanes such as the Fiat G.50, but being short on funds, were forced to continue operating obsolete Fiat CR.42 biplanes.
From the early 1930s the Japanese had been at war against both the Chinese Nationalists and the Russians in China, and used the experience to improve both training and aircraft, replacing biplanes with modern cantilever monoplanes and creating a cadre of exceptional pilots for use in the Pacific War. In the United Kingdom, at the behest of Neville Chamberlain, (more famous for his 'peace in our time' speech) the entire British aviation industry was retooled, allowing it to change quickly from fabric covered metal framed biplanes to cantilever stressed skin monoplanes in time for the war with Germany.
The period of improving the same biplane design over and over was now coming to an end, and the Hawker Hurricane and Supermarine Spitfire finally started to supplant the Gloster Gladiator and Hawker Fury biplanes but many of the former remained in front-line service well past the start of World War II. While not a combatant themselves in Spain, they absorbed many of the lessons learned in time to use them.
The Spanish Civil War also provided an opportunity for updating fighter tactics. One of the innovations to result from the aerial warfare experience this conflict provided was the development of the "finger-four" formation by the German pilot Werner Mölders. Each fighter squadron (German: Staffel) was divided into several flights (Schwärme) of four aircraft. Each Schwarm was divided into two Rotten, which was a pair of aircraft. Each Rotte was composed of a leader and a wingman. This flexible formation allowed the pilots to maintain greater situational awareness, and the two Rotten could split up at any time and attack on their own. The finger-four would become widely adopted as the fundamental tactical formation over the course of World War.[clarification needed]
World War II 
The Second World War featured fighter combat on a larger scale than any other conflict to date. German Field Marshal Erwin Rommel noted the effect of airpower: "Anyone who has to fight, even with the most modern weapons, against an enemy in complete command of the air, fights like a savage against modern European troops, under the same handicaps and with the same chances of success." Throughout the conflict, fighters performed their conventional role in establishing air superiority through combat with other fighters and through bomber interception, and many fighters were also pressed into service in additional roles such as tactical air support and reconnaissance.
The approach of different belligerents to fighter design varied widely, with the Japanese and Italians favoring lightly armed and armored but highly maneuverable designs such as the Japanese Nakajima Ki-27, Nakajima Ki-43 and Mitsubishi A6M Zero and Italy's Fiat G.50 and Macchi MC.200. In contrast, designers in Great Britain, Germany, the Soviet Union, and the United States believed that due to the increasing speed of fighter aircraft, the twisting and maneuvering typical of World War I dogfights would create g-forces unbearable to pilots. These nations' fighters instead were optimized for speed and firepower to allow pilots to quickly engage, dispatch and disengage with opposing aircraft. While light, highly maneuverable aircraft did have some advantages in fighter-versus-fighter combat, those could usually be overcome by sound tactical doctrine, and the design approach of the Italians and Japanese made their planes ill-suited as interceptors or attack aircraft.
European theater 
During the invasion of Poland and the Battle of France, Luftwaffe fighters—primarily the Messerschmitt Bf 109—held air superiority, and the Luftwaffe played a major role in German victories in these campaigns. During the Battle of Britain, however, British Hurricanes and Spitfires proved roughly equal to Luftwaffe fighters. Additionally Britain's use of radar and the advantages of fighting above Britain's home territory allowed the RAF to deny Germany air superiority, saving Britain from German invasion and dealing the Axis their first major defeat of the Second World War.
On the Eastern Front, Soviet fighter forces were overwhelmed during the opening phases of Operation Barbarossa. This was a result of the tactical surprise at the outset of the campaign, the leadership vacuum within the Soviet military left by the Great Purge, and the general inferiority of Soviet designs at the time, such as the obsolescent I-15 biplane and the I-16. More modern Soviet designs, including the MiG-3, LaGG-3 and Yak-1, had not yet arrived in numbers and in any case were still inferior to the Messerschmitt Bf 109. As a result, during the early months of these campaigns, Axis air forces destroyed large numbers of Red Air Force aircraft on the ground and in one-sided dogfights.
In the later stages on the Eastern Front, Soviet training and leadership improved, as did their equipment. Late-war Soviet designs such as the Yakovlev Yak-3 and Lavochkin La-7 had performance comparable to the German Bf-109 and Focke-Wulf Fw 190. Also, significant numbers of British, and later U.S., fighter aircraft were supplied to aid the Soviet war effort as part of Lend-Lease, with the Bell P-39 Airacobra proving particularly effective in the lower-altitude combat typical of the Eastern Front. The Soviets were also helped indirectly by the American and British bombing campaigns, which forced the Luftwaffe to shift many of its fighters away from the Eastern Front in defense against these raids. The Soviets increasingly were able to challenge the Luftwaffe, and while the Luftwaffe maintained a qualitative edge over the Red Air Force for much of the war, the increasing numbers and efficacy of the Soviet Air Force were critical to the Red Army's efforts at turning back and eventually annihilating the Wehrmacht.
Meanwhile air combat on the Western Front had a much different character. Much of this combat was centered around the strategic bombing campaigns of the RAF and the USAAF. Axis fighter aircraft focused on defending against Allied bombers while Allied fighters' main role was as bomber escorts. The RAF raided German cities at night, and both sides developed radar-equipped night fighters for these battles. The Americans, in contrast, flew daylight bombing raids into Germany. Unescorted B-24 and B-17 bombers, however, proved unable to fend off German interceptors (primarily Bf-109s and FW-190s). With the later arrival of long range fighters, particularly the P-51, U.S. fighters were able to escort daylight raids far into Germany and establish control of the skies over Western Europe.
By the time of Operation Overlord in June 1944, the Allies had gained near complete air superiority over the Western Front. This cleared the way both for intensified strategic bombing of German cities and industries, and for the tactical bombing of battlefield targets. With the Luftwaffe largely cleared from the skies, Allied fighters increasingly served as attack aircraft.
Allied fighters, by gaining air superiority over the European battlefield, played a crucial role in the eventual defeat of the Axis, which Reichmarshal Hermann Göring, commander of the German Luftwaffe summed up when he said: "When I saw Mustangs over Berlin, I knew the jig was up."
Pacific theater 
Major air combat during the war in the Pacific began with the entry of the Western Allies following Japan's attack against Pearl Harbor. The Imperial Japanese Navy Air Service primarily operating the Mitsubishi A6M Zero, and the Imperial Japanese Army Air Service flying the Nakajima Ki-27 and the Nakajima Ki-43, initially enjoyed great success, as these fighters generally had better range, maneuverability, speed and climb rates than their Allied counterparts. Additionally, Japanese pilots had received excellent training and many were combat veterans from Japan's campaigns in China. They quickly gained air superiority over the Allies, who at this stage of the war were often disorganized, under-trained and poorly equipped, and Japanese air power contributed significantly to their successes in the Philippines, Malaysia and Singapore, the Dutch East Indies and Burma.
By mid-1942, the Allies began to regroup and while some Allied aircraft such as the Brewster Buffalo and the P-39 were hopelessly outclassed by fighters like Japan's Zero, others such as the Army's P-40 and the Navy's Wildcat possessed attributes such as superior firepower, ruggedness and dive speed, and the Allies soon developed tactics (such as the Thach weave) to take advantage of these strengths. These changes soon paid dividends, as the Allied ability to deny Japan air superiority was critical to their victories at Coral Sea, Midway, Guadalcanal and New Guinea. In China, the Flying Tigers also used the same tactics with some success, although they were unable to stem the tide of Japanese advances there.
By 1943, the Allies began to gain the upper hand in the Pacific Campaign's air campaigns. Several factors contributed to this shift. First, second-generation Allied fighters such as the Hellcat and the P-38, and later the Corsair, the P-47 and the P-51, began arriving in numbers. These fighters outperformed Japanese fighters in all respects except maneuverability. Other problems with Japan's fighter aircraft also became apparent as the war progressed, such as their lack of armor and light armament, which made them inadequate as bomber interceptors or ground-attack planes—roles Allied fighters excelled at. Additionally, Japan's training program failed to provide enough well-trained pilots to replace losses. In contrast, the Allies improved both the quantity and quality of pilots graduating from their training programs.
By mid-1944, Allied fighters had gained air superiority throughout the theater, which would not be contested again during the war. The extent of Allied quantitative and qualitative superiority by this point in the war was demonstrated during Battle of the Philippine Sea, a lopsided Allied victory where Japanese fliers were downed in such numbers and with such ease that American fighter pilots likened it to a great turkey shoot.
Late in the war, Japan did begin to produce new fighters such as the Nakajima Ki-84 and the Kawanishi N1K to replace the venerable Zero, but these were produced only in small numbers, and in any case by that time Japan lacked trained pilots or sufficient fuel to mount a sustained challenge to Allied fighters. During the closing stages of the war, Japan's fighter arm could not seriously challenge raids over Japan by American B-29s, and was largely relegated to Kamikaze tactics.
Technological innovations 
Fighter technology advanced rapidly during the Second World War. Piston-engines, which powered the vast majority of World War II fighters, grew more powerful: at the beginning of the war fighters typically had engines producing between 1,000 hp (750 kW) and 1,400 hp (1,000 kW), while by the end of the war many could produce over 2,000 hp (1,500 kW). For example, the Spitfire, one of the few fighters in continuous production throughout the war, was in 1939 powered by a 1,030 hp (770 kW) Merlin II, while variants produced in 1945 were equipped with the 2,035 hp (1,517 kW) Griffon 61. Nevertheless, these fighters could only achieve modest increases in top speed due to problems of compressibility created as aircraft and their propellers approached the sound barrier, and it was apparent that propeller-driven aircraft were approaching the limits of their performance. German jet and rocket powered fighters entered combat in 1944, although too late to impact the war's outcome.
World War II fighters also increasingly featured monocoque construction, which improved their aerodynamic efficiency while also adding structural strength. Laminar flow wings, which improved high speed performance, also came into use on fighters such as the P-51, while the Messerschmitt Me 262 and the Messerschmitt Me 163 featured swept wings that dramatically reduced drag at high subsonic speeds.
Armament also advanced during the war. The rifle-caliber machine guns that were common on prewar fighters could not easily down the more rugged warplanes of the era. Air forces began to replace or supplement them with cannons, which fired explosive shells that could blast a hole in an enemy aircraft—rather than relying on kinetic energy from a solid bullet striking a fuel line, control cable, pilot, etc. Cannons could bring down even heavy bombers with just a few hits, but their slower rate of fire made it difficult to hit fast moving fighters in a dogfight. Eventually, most fighters mounted cannons, sometimes in combination with machine guns.
The British epitomized this shift. Their standard early war fighters mounted eight .303-inch (7.7 mm) calibre machine guns—whereas by mid-war they often featured a combination of machine guns and 20 mm cannons, and late in the war often only cannons. The Americans, in contrast, had problems designing a native cannon design, so instead placed multiple .50 caliber (12.7 mm) heavy machine guns on their fighters. Fighters were also increasingly fitted with bomb racks and air-to-surface ordnance such as bombs or rockets beneath the their wings, and pressed into close air support roles as fighter-bombers. Although they carried less ordnance than light and medium bombers, they were cheaper to produce and maintain and their maneuverability made it easier for them to hit moving targets such as motorized vehicles. Moreover, if they encountered enemy fighters, their ordnance (which reduced lift and increased drag and therefore decreased performance) could be jettisoned and they could engage the enemy fighters, which eliminated the need for fighter escorts that bombers required. Heavily armed and sturdily constructed fighters such as Germany's Focke-Wulf Fw 190, Britain's Hawker Typhoon and Hawker Tempest, and America's P-40, Corsair, P-47 and P-38 all excelled as fighter-bombers, and since the Second World War ground attack has been an important secondary capability of many fighters.
World War II also saw the first use of airborne radar on fighters. The primary purpose of these radars was to help night fighters locate enemy bombers and fighters. Because of the bulkiness of these radar sets, they could not be carried on conventional single-engined fighters and instead were typically retrofitted to larger heavy fighters or light bombers such as Germany's Messerschmitt Bf 110 and Junkers Ju 88, Britain's Mosquito and Beaufighter, and America's A-20, which then served as night fighters. The Northrop P-61 Black Widow, a purpose-built night fighter, was the only fighter of the war that incorporated radar into its original design. Britain and America cooperated closely in the development of airborne radar, and Germany's radar technology generally lagged slightly behind Anglo-American efforts, while other combatants developed few radar-equipped fighters.
Post–World War II period 
Several prototype fighter programs begun early in 1945 continued on after the war and led to advanced piston-engine fighters that entered production and operational service in 1946. A typical example is the Lavochkin La-9 'Fritz', which was an evolution of the successful wartime Lavochkin La-7 'Fin'. Working through a series of prototypes, the La-120, La-126 and La-130, the Lavochkin design bureau sought to replace the La-7's wooden airframe with a metal one, as well as fit a laminar-flow wing to improve maneuver performance, and increased armament. The La-9 entered service in August 1946 and was produced until 1948; it also served as the basis for the development of a long-range escort fighter, the La-11 'Fang', of which nearly 1200 were produced 1947–1951. Over the course of the Korean War, however, it became obvious that the day of the piston-engined fighter was coming to a close and that the future would lie with the jet fighter.
This period also witnessed experimentation with jet-assisted piston engine aircraft. La-9 derivatives included examples fitted with two underwing auxiliary pulsejet engines (the La-9RD) and a similarly mounted pair of auxiliary ramjet engines (the La-138); however, neither of these entered service. One that did enter service – with the U.S. Navy in March 1945 – was the Ryan FR-1 Fireball; production was halted with the war's end on VJ-Day, with only 66 having been delivered, and the type was withdrawn from service in 1947. The USAAF had ordered its first 13 mixed turboprop-turbojet-powered pre-production prototypes of the Consolidated Vultee XP-81 fighter, but this program was also canceled by VJ Day, with 80% of the engineering work completed.
Rocket-powered fighters 
The first rocket-powered aircraft was the Lippisch Ente, which made a successful maiden flight in March 1928. The only pure rocket aircraft ever mass-produced was the Messerschmitt Me 163 in 1944, one of several German World War II projects aimed at developing rocket-powered aircraft. Later variants of the Me 262 (C-1a and C-2b) were also fitted with rocket powerplants, while earlier models were fitted with rocket boosters, but were not mass-produced with these modifications.
The USSR experimented with a rocket-powered interceptor in the years immediately following World War II, the Mikoyan-Gurevich I-270. Only two were built.
In the 1950s, the British developed mixed-power jet designs employing both rocket and jet engines to cover the performance gap that existed in turbojet designs. The rocket was the main engine for delivering the speed and height required for high-speed interception of high-level bombers and the turbojet gave increased fuel economy in other parts of flight, most notably to ensure the aircraft was able to make a powered landing rather than risking an unpredictable gliding return. The Saunders-Roe SR.53 was a successful design, and was planned for production when economics forced the British to curtail most aircraft programs in the late 1950s. Furthermore, rapid advancements in jet engine technology rendered mixed-power aircraft designs like Saunders-Roe's SR.53 (and its SR.177 maritime variant) obsolete. The American XF-91 Thunderceptor (the first U.S. fighter to exceed Mach 1 in level flight) met a similar fate for the same reason, and no hybrid rocket-and-jet-engine fighter design has ever been placed into service. The only operational implementation of mixed propulsion was Rocket-Assisted Take Off (RATO), a system rarely used in fighters.
Jet-powered fighters 
It has become common in the aviation community to classify jet fighters by "generations" for historical purposes. There are no official definitions of these generations; rather, they represent the notion that there are stages in the development of fighter design approaches, performance capabilities, and technological evolution. Also other authors have packed the fighters into different generations. For example Richard P. Hallion of the Secretary of the Air Force's Action Group classified the F-16 as a sixth generation jet fighter.
The timeframes associated with each generation are inexact and are only indicative of the period during which their design philosophies and technology employment enjoyed a prevailing influence on fighter design and development. These timeframes also encompass the peak period of service entry for such aircraft.
First generation subsonic jet fighters (mid-1940s to mid-1950s) 
The first generation of jet fighters comprised the initial, subsonic jet fighter designs introduced late in World War II and in the early post-war period. They differed little from their piston-engined counterparts in appearance, and many employed unswept wings. Guns remained the principal armament. The need to obtain a decisive advantage in maximum speed pushed the development of turbojet-powered aircraft forward. Top speeds for fighters rose steadily throughout World War II as more powerful piston engines were developed, and was approaching transonic flight speeds where the efficiency of propellers drops off, making further speed increases nearly impossible.
The first jets were developed during World War II and saw combat in the last two years of the war. Messerschmitt developed the first operational jet fighter, the Me 262. It was considerably faster than contemporary piston-driven aircraft, and in the hands of a competent pilot, was quite difficult for Allied pilots to defeat. The design was never deployed in numbers sufficient to stop the Allied air campaign, and a combination of fuel shortages, pilot losses, and technical difficulties with the engines kept the number of sorties low. Nevertheless, the Me 262 indicated the obsolescence of piston-driven aircraft. Spurred by reports of the German jets, Britain's Gloster Meteor entered production soon after and the two entered service around the same time in 1944. Meteors were commonly used to intercept the V-1 "buzz bomb", as they were faster than available piston-engined fighters. By the end of the war almost all work on piston-powered fighters had ended. A few designs combining piston and jet engines for propulsion – such as the Ryan FR Fireball – saw brief use, but by the end of the 1940s virtually all new fighters were jet-powered.
Despite their advantages, the early jet fighters were far from perfect. The operational lifespan of turbines were very short and engines were temperamental, while power could be adjusted only slowly and acceleration was poor (even if top speed was higher) compared to the final generation of piston fighters. Many squadrons of piston-engined fighters were retained until the early to mid-1950s, even in the air forces of the major powers (though the types retained were the best of the World War II designs). Innovations including ejection seats, air brakes and all-moving tailplanes became widespread in this period.
The Americans begin using jet fighters operationally post-war, the wartime Bell P-59 having proven itself a failure. The Lockheed P-80 Shooting Star (soon re-designated F-80) was less elegant than the swept-wing Me 262, but had a cruise speed (660 km/h (410 mph)]) as high as the maximum speed attainable by many piston-engined fighters. The British designed several new jets, including the distinctive twin boom de Havilland Vampire which was sold to the air forces of many nations.
The British transferred the technology of the Rolls-Royce Nene jet engine to the Soviets, who soon put it to use in their advanced Mikoyan-Gurevich MiG-15 fighter, which used fully swept wings that allowed flying closer to the speed of sound than straight-winged designs such as the F-80. Its top speed of 1,075 km/h (668 mph) proved quite a shock to the American F-80 pilots who encountered them over Korea, along with their armament of two 23 mm cannons and a single 37 mm cannon. Nevertheless, in the first jet-versus-jet dogfight, which occurred during the Korean War on 8 November 1950, an F-80 downed two North Korean MiG-15s.
The Americans responded by rushing their own swept-wing F-86 into battle against the MiGs, which had similar transsonic performance. The two aircraft had different strengths and weaknesses, but were similar enough that victory could go either way. While the Sabres were focussed primarily on downing MiGs and scored favourably against those flown by the poorly trained North Koreans, the MiGs in turn decimated US bomber formations and forced the withdrawal of numerous American types from operational service.
The world's navies also transitioned to jets during this period, despite the need for catapult-launching of the new aircraft. Grumman's F9F Panther was adopted by the U.S. Navy as their primary jet fighter in the Korean War period, and it was one of the first jet fighters to employ an afterburner. The de Havilland Sea Vampire was the Royal Navy's first jet fighter. Radar was used on specialized night fighters such as the F3D Skyknight, which also downed MiGs over Korea, and later fitted to the F2H Banshee and swept wing F7U Cutlass and F3H Demon as all-weather / night fighters. Early versions of Infra-red (IR) air-to-air missiles (AAMs) such as the AIM-9 Sidewinder and radar guided missiles such as the AIM-7 Sparrow whose descendants are still in use, were first introduced on swept wing subsonic Demon and Cutlass naval fighters.
Second generation jet fighters (mid-1950s to early 1960s) 
The development of second-generation fighters was shaped by technological breakthroughs, lessons learned from the aerial battles of the Korean War, and a focus on conducting operations in a nuclear warfare environment. Technological advances in aerodynamics, propulsion and aerospace building materials (primarily aluminium alloys) permitted designers to experiment with aeronautical innovations, such as swept wings, delta wings, and area-ruled fuselages. Widespread use of afterburning turbojet engines made these the first production aircraft to break the sound barrier, and the ability to sustain supersonic speeds in level flight became a common capability amongst fighters of this generation.
Fighter designs also took advantage of new electronics technologies that made effective radars small enough to carry aboard smaller aircraft. Onboard radars permitted detection of enemy aircraft beyond visual range, thereby improving the handoff of targets by longer-ranged ground-based warning and tracking radars. Similarly, advances in guided missile development allowed air-to-air missiles to begin supplementing the gun as the primary offensive weapon for the first time in fighter history. During this period, passive-homing infrared-guided (IR) missiles became commonplace, but early IR missile sensors had poor sensitivity and a very narrow field of view (typically no more than 30°), which limited their effective use to only close-range, tail-chase engagements. Radar-guided (RF) missiles were introduced as well, but early examples proved unreliable. These semi-active radar homing (SARH) missiles could track and intercept an enemy aircraft "painted" by the launching aircraft's onboard radar. Medium- and long-range RF air-to-air missiles promised to open up a new dimension of "beyond-visual-range" (BVR) combat, and much effort was placed in further development of this technology.
The prospect of a potential third world war featuring large mechanized armies and nuclear weapon strikes led to a degree of specialization along two design approaches: interceptors, such as the English Electric Lightning and Mikoyan-Gurevich MiG-21F; and fighter-bombers, such as the Republic F-105 Thunderchief and the Sukhoi Su-7B. Dogfighting, per se, was de-emphasized in both cases. The interceptor was an outgrowth of the vision that guided missiles would completely replace guns and combat would take place at beyond visual ranges. As a result, interceptors were designed with a large missile payload and a powerful radar, sacrificing agility in favor of high speed, altitude ceiling and rate of climb. With a primary air defense role, emphasis was placed on the ability to intercept strategic bombers flying at high altitudes. Specialized point-defense interceptors often had limited range and little, if any, ground-attack capabilities. Fighter-bombers could swing, between air superiority and ground-attack roles, and were often designed for a high-speed, low-altitude dash to deliver their ordnance. Television- and IR-guided air-to-surface missiles were introduced to augment traditional gravity bombs, and some were also equipped to deliver a nuclear bomb.
Third generation jet fighters (early 1960s to circa 1970) 
The third generation witnessed continued maturation of second-generation innovations, but it is most marked by renewed emphases on maneuverability and traditional ground-attack capabilities. Over the course of the 1960s, increasing combat experience with guided missiles demonstrated that combat would devolve into close-in dogfights. Analog avionics began to appear, replacing older "steam-gauge" cockpit instrumentation. Enhancements to the aerodynamic performance of third-generation fighters included flight control surfaces such as canards, powered slats, and blown flaps. A number of technologies would be tried for Vertical/Short Takeoff and Landing, but thrust vectoring would be successful on the Harrier.
Growth in air combat capability focused on the introduction of improved air-to-air missiles, radar systems, and other avionics. While guns remained standard equipment (early models of F-4 being a notable exception), air-to-air missiles became the primary weapons for air superiority fighters, which employed more sophisticated radars and medium-range RF AAMs to achieve greater "stand-off" ranges, however, kill probabilities proved unexpectedly low for RF missiles due to poor reliability and improved electronic countermeasures (ECM) for spoofing radar seekers. Infrared-homing AAMs saw their fields of view expand to 45°, which strengthened their tactical usability. Nevertheless, the low dogfight loss-exchange ratios experienced by American fighters in the skies over Vietnam led the U.S. Navy to establish its famous "TOPGUN" fighter weapons school, which provided a graduate-level curriculum to train fleet fighter pilots in advanced Air Combat Maneuvering (ACM) and Dissimilar Air Combat Training (DACT) tactics and techniques.
This era also saw an expansion in ground-attack capabilities, principally in guided missiles, and witnessed the introduction of the first truly effective avionics for enhanced ground attack, including terrain-avoidance systems. Air-to-surface missiles (ASM) equipped with electro-optical (E-O) contrast seekers – such as the initial model of the widely used AGM-65 Maverick – became standard weapons, and laser-guided bombs (LGBs) became widespread in effort to improve precision-attack capabilities. Guidance for such precision-guided munitions (PGM) was provided by externally mounted targeting pods, which were introduced in the mid-1960s.
It also led to the development of new automatic-fire weapons, primarily chain-guns that use an electric engine to drive the mechanism of a cannon. This allowed a plane to carry a single multi-barrel weapon (such as the 20 mm Vulcan), and provided greater accuracy and rates of fire. Powerplant reliability increased and jet engines became "smokeless" to make it harder to sight aircraft at long distances.
Dedicated ground-attack aircraft (like the Grumman A-6 Intruder, SEPECAT Jaguar and LTV A-7 Corsair II) offered longer range, more sophisticated night attack systems or lower cost than supersonic fighters. With variable-geometry wings, the supersonic F-111 introduced the Pratt & Whitney TF30, the first turbofan equipped with afterburner. The ambitious project sought to create a versatile common fighter for many roles and services. It would serve well as an all-weather bomber, but lacked the performance to defeat other fighters. The McDonnell F-4 Phantom was designed around radar and missiles as an all-weather interceptor, but emerged as a versatile strike bomber nimble enough to prevail in air combat, adopted by the U.S. Navy, Air Force and Marine Corps. Despite numerous shortcomings that would be not be fully addressed until newer fighters, the Phantom claimed 280 aerial kills, more than any other U.S. fighter over Vietnam. With range and payload capabilities that rivaled that of World War II bombers such as B-24 Liberator, the Phantom would became a highly successful multirole aircraft.
Fourth generation jet fighters (circa 1970 to mid-1990s) 
Fourth-generation fighters continued the trend towards multirole configurations, and were equipped with increasingly sophisticated avionics and weapon systems. Fighter designs were significantly influenced by the Energy-Maneuverability (E-M) theory developed by Colonel John Boyd and mathematician Thomas Christie, based upon Boyd's combat experience in the Korean War and as a fighter tactics instructor during the 1960s. E-M theory emphasized the value of aircraft specific energy maintenance as an advantage in fighter combat. Boyd perceived maneuverability as the primary means of getting "inside" an adversary's decision-making cycle, a process Boyd called the "OODA loop" (for "Observation-Orientation-Decision-Action"). This approach emphasized aircraft designs that were capable of performing "fast transients" – quick changes in speed, altitude, and direction – as opposed to relying chiefly on high speed alone.
E-M characteristics were first applied to the McDonnell Douglas F-15 Eagle, but Boyd and his supporters believed these performance parameters called for a small, lightweight aircraft with a larger, higher-lift wing. The small size would minimize drag and increase the thrust-to-weight ratio, while the larger wing would minimize wing loading; while the reduced wing loading tends to lower top speed and can cut range, it increases payload capacity and the range reduction can be compensated for by increased fuel in the larger wing. The efforts of Boyd's "Fighter Mafia" would result in the General Dynamics F-16 Fighting Falcon (now Lockheed Martin's).
The F-16's maneuverability was further enhanced by its slight aerodynamic instability. This technique, called "relaxed static stability" (RSS), was made possible by introduction of the "fly-by-wire" (FBW) flight control system (FLCS), which in turn was enabled by advances in computers and system integration techniques. Analog avionics, required to enable FBW operations, became a fundamental requirement and began to be replaced by digital flight control systems in the latter half of the 1980s. Likewise, Full Authority Digital Engine Controls (FADEC) to electronically manage powerplant performance was introduced with the Pratt & Whitney F100 turbofan. The F-16's sole reliance on electronics and wires to relay flight commands, instead of the usual cables and mechanical linkage controls, earned it the sobriquet of "the electric jet". Electronic FLCS and FADEC quickly became essential components of all subsequent fighter designs.
Other innovative technologies introduced in fourth-generation fighters include pulse-Doppler fire-control radars (providing a "look-down/shoot-down" capability), head-up displays (HUD), "hands on throttle-and-stick" (HOTAS) controls, and multi-function displays (MFD), all now essential equipment. Aircraft designers began to incorporate composite materials in the form of bonded aluminum honeycomb structural elements and graphite epoxy laminate skins to reduce weight. Infrared search-and-track (IRST) sensors became widespread for air-to-ground weapons delivery, and appeared for air-to-air combat as well. "All-aspect" IR AAM became standard air superiority weapons, which permitted engagement of enemy aircraft from any angle (although the field of view remained relatively limited). The first long-range active-radar-homing RF AAM entered service with the AIM-54 Phoenix, which solely equipped the Grumman F-14 Tomcat, one of the few variable-sweep-wing fighter designs to enter production. Even with the tremendous advancement of Air to Air missiles in this era, internal guns were standard equipment.
Another revolution came in the form of a stronger reliance on ease of maintenance, which led to standardisation of parts, reductions in the numbers of access panels and lubrication points, and overall parts reduction in more complicated equipment like the engines. Some early jet fighters required 50 man-hours of work by a ground crew for every hour the aircraft was in the air; later models substantially reduced this to allow faster turn-around times and more sorties in a day. Some modern military aircraft only require 10 man-hours of work per hour of flight time, and others are even more efficient.
Aerodynamic innovations included variable-camber wings and exploitation of the vortex lift effect to achieve higher angles of attack through the addition of leading-edge extension devices such as strakes.
Unlike interceptors of the previous eras, most fourth-generation air-superiority fighters were designed to be agile dogfighters (although the Mikoyan MiG-31 and Panavia Tornado ADV are notable exceptions). The continually rising cost of fighters, however, continued to emphasize the value of multirole fighters. The need for both types of fighters led to the "high/low mix" concept, which envisioned a high-capability and high-cost core of dedicated air-superiority fighters (like the F-15 and Su-27) supplemented by a larger contingent of lower-cost multi-role fighters (such as the F-16 and MiG-29).
Most fourth-generation fighters, such as the McDonnell Douglas F/A-18 Hornet and Dassault Mirage 2000, are true multirole warplanes, designed as such from the start. This was facilitated by multimode avionics that could switch seamlessly between air and ground modes. The earlier approaches of adding on strike capabilities or designing separate models specialized for different roles generally became passé (with the Panavia Tornado being an exception in this regard). Attack roles were generally assigned to dedicated ground-attack aircraft such as the Sukhoi Su-24 and the A-10 Thunderbolt II.
Perhaps the most novel technology introduced for combat aircraft was stealth, which involves the use of special "low-observable" (L-O) materials and design techniques to reduce the susceptibility of an aircraft to detection by the enemy's sensor systems, particularly radars. The first stealth aircraft introduced were the Lockheed F-117 Nighthawk attack aircraft (introduced in 1983) and the Northrop Grumman B-2 Spirit bomber (which first flew in 1989). Although no stealthy fighters per se appeared among the fourth generation, some radar-absorbent coatings and other L-O treatments developed for these programs are reported to have been subsequently applied to fourth-generation fighters.
4.5th generation jet fighters (1990s to present) 
The end of the Cold War in 1991 led many governments to significantly decrease military spending as a "peace dividend". Air force inventories were cut. Research and development programs working on "fifth-generation" fighters took serious hits. Many programs were canceled during the first half of the 1990s, and those that survived were "stretched out". While the practice of slowing the pace of development reduces annual investment expenses, it comes at the penalty of increased overall program and unit costs over the long-term. In this instance, however, it also permitted designers to make use of the tremendous achievements being made in the fields of computers, avionics and other flight electronics, which had become possible largely due to the advances made in microchip and semiconductor technologies in the 1980s and 1990s. This opportunity enabled designers to develop fourth-generation designs – or redesigns – with significantly enhanced capabilities. These improved designs have become known as "Generation 4.5" fighters, recognizing their intermediate nature between the 4th and 5th generations, and their contribution in furthering development of individual fifth-generation technologies.
The primary characteristics of this sub-generation are the application of advanced digital avionics and aerospace materials, modest signature reduction (primarily RF "stealth"), and highly integrated systems and weapons. These fighters have been designed to operate in a "network-centric" battlefield environment and are principally multirole aircraft. Key weapons technologies introduced include beyond-visual-range (BVR) AAMs; Global Positioning System (GPS)-guided weapons, solid-state phased-array radars; helmet-mounted sights; and improved secure, jamming-resistant datalinks. Thrust vectoring to further improve transient maneuvering capabilities has also been adopted by many 4.5th generation fighters, and uprated powerplants have enabled some designs to achieve a degree of "supercruise" ability. Stealth characteristics are focused primarily on frontal-aspect radar cross section (RCS) signature-reduction techniques including radar-absorbent materials (RAM), L-O coatings and limited shaping techniques.
"Half-generation" designs are either based on existing airframes or are based on new airframes following similar design theory as previous iterations; however, these modifications have introduced the structural use of composite materials to reduce weight, greater fuel fractions to increase range, and signature reduction treatments to achieve lower RCS compared to their predecessors. Prime examples of such aircraft, which are based on new airframe designs making extensive use of carbon-fibre composites, include the Eurofighter Typhoon, Dassault Rafale, and Saab JAS 39 Gripen.
Apart from these fighter jets, most of the 4.5 generation aircraft are actually modified variants of existing airframes from the earlier fourth generation fighter jets. Such fighter jets are generally heavier and examples include the Boeing F/A-18E/F Super Hornet, which is an evolution of the 1970s F/A-18 Hornet design, the F-15E Strike Eagle, which is a ground-attack/multi-role variant of the F-15 Eagle, the Su-30MKI and Su-30MKK variants of the Sukhoi Su-30 and the MiG-29M, MiG-29K and MiG-35, upgraded versions of the Mikoyan MiG-29. The Su-30MKI and MiG-35 feature thrust vectoring engine nozzles to enhance maneuvering.
4.5 generation fighters first entered service in the early 1990s, and most of them are still being produced and evolved. It is quite possible that they may continue in production alongside fifth-generation fighters due to the expense of developing the advanced level of stealth technology needed to achieve aircraft designs featuring very low observables (VLO), which is one of the defining features of fifth-generation fighters. Of the 4.5th generation designs, the Strike Eagle, Super Hornet, Typhoon, Gripen, and Rafale have been used in combat.
The U.S. government has defined 4.5 generation fighter aircraft as those that "(1) have advanced capabilities, including— (A) AESA radar; (B) high capacity data-link; and (C) enhanced avionics; and (2) have the ability to deploy current and reasonably foreseeable advanced armaments."
Fifth generation jet fighters (2005 to the present) 
The fifth generation was ushered in by the Lockheed Martin/Boeing F-22 Raptor in late 2005. Currently the cutting edge of fighter design, fifth-generation fighters are characterized by being designed from the start to operate in a network-centric combat environment, and to feature extremely low, all-aspect, multi-spectral signatures employing advanced materials and shaping techniques. They have multifunction AESA radars with high-bandwidth, low-probability of intercept (LPI) data transmission capabilities. The Infra-red search and track sensors incorporated for air-to-air combat as well as for air-to-ground weapons delivery in the 4.5th generation fighters are now fused in with other sensors for Situational Awareness IRST or SAIRST, which constantly tracks all targets of interest around the aircraft so the pilot need not guess when he glances. These sensors, along with advanced avionics, glass cockpits, helmet-mounted sights (not currently on F-22), and improved secure, jamming-resistant LPI datalinks are highly integrated to provide multi-platform, multi-sensor data fusion for vastly improved situational awareness while easing the pilot's workload. Avionics suites rely on extensive use of very high-speed integrated circuit (VHSIC) technology, common modules, and high-speed data buses. Overall, the integration of all these elements is claimed to provide fifth-generation fighters with a "first-look, first-shot, first-kill capability".
The AESA radar offers unique capabilities for fighters (and it is also quickly becoming essential for Generation 4.5 aircraft designs, as well as being retrofitted onto some fourth-generation aircraft). In addition to its high resistance to ECM and LPI features, it enables the fighter to function as a sort of "mini-AWACS," providing high-gain electronic support measures (ESM) and electronic warfare (EW) jamming functions.
Other technologies common to this latest generation of fighters includes integrated electronic warfare system (INEWS) technology, integrated communications, navigation, and identification (CNI) avionics technology, centralized "vehicle health monitoring" systems for ease of maintenance, fiber optics data transmission, stealth technology and even hovering capabilities. Maneuver performance remains important and is enhanced by thrust-vectoring, which also helps reduce takeoff and landing distances. Supercruise may or may not be featured; it permits flight at supersonic speeds without the use of the afterburner – a device that significantly increases IR signature when used in full military power.
A key attribute of fifth-generation fighters is a small radar cross-section. Great care has been taken in designing its layout and internal structure to minimize RCS over a broad bandwidth of detection and tracking radar frequencies; furthermore, to maintain its VLO signature during combat operations, primary weapons are carried in internal weapon bays that are only briefly opened to permit weapon launch. Furthermore, stealth technology has advanced to the point where it can be employed without a tradeoff with aerodynamics performance, in contrast to previous stealth efforts. Some attention has also been paid to reducing IR signatures, especially on the F-22. Detailed information on these signature-reduction techniques is classified, but in general includes special shaping approaches, thermoset and thermoplastic materials, extensive structural use of advanced composites, conformal sensors, heat-resistant coatings, low-observable wire meshes to cover intake and cooling vents, heat ablating tiles on the exhaust troughs (seen on the Northrop YF-23), and coating internal and external metal areas with radar-absorbent materials and paint (RAM/RAP).
Such aircraft are sophisticated and expensive. The U.S. Air Force originally planned to acquire 650 F-22s, but now only 187 will be built. As a result, its unit flyaway cost (FAC) is around US$150 million. To spread the development costs – and production base – more broadly, the Joint Strike Fighter (JSF) program enrolls eight other countries as cost- and risk-sharing partners. Altogether, the nine partner nations anticipate procuring over 3,000 Lockheed Martin F-35 Lightning II fighters at an anticipated average FAC of $80–85 million. The F-35, however, is designed to be a family of three aircraft, a conventional take-off and landing (CTOL) fighter, a short take-off and vertical landing (STOVL) fighter, and a Catapult Assisted Take Off But Arrested Recovery (CATOBAR) fighter, each of which has a different unit price and slightly varying specifications in terms of fuel capacity (and therefore range), size and payload.
Other countries have initiated fifth-generation fighter development projects, with Russia's Sukhoi PAK FA and Mikoyan LMFS. In October 2007, Russia and India signed an agreement for joint participation in a Fifth-Generation Fighter Aircraft Program (FGFA), which gives India responsibility for development of a two-seat model of the PAK-FA. In December 2010, it was discovered that China is developing the 5th generation fighter Chengdu J-20. The J-20 took its maiden flight in January 2011 and is planned to be deployed in 2017–19 time frame. Another Chinese stealth fighter J-31 took its maiden flight on 31 October 2012. India is also developing its own indigenous fifth generation aircraft named Medium Combat Aircraft. Japan is exploring its technical feasibility to produce fifth-generation fighters.
Sixth generation jet fighters 
A sixth generation jet fighter is a conceptual airplane expected to enter service in the United States Air Force and United States Navy in 2025–30 timeframe. With the Chinese J-20 and the Russian PAK FA under development, the need for a sixth-generation fighter may be urgent for the US military. The USAF seeks new fighter for the 2030–50 period named the "Next Generation Tactical Aircraft"/"Next Gen TACAIR" The US Navy looks to replace its F/A-18E/F Super Hornets beginning in 2025 with the Next Generation Air Dominance air superiority fighter.
See also 
- "Fighter —Definition and More from the Free Merriam Webster Dictionary.". Merriam Webster Dictionary. Encyclopædia Britannica. 22 September 2011.
- Andreas Parsch (22 September 2011). "Non-Standard DOD Aircraft Designations".
- "Mitchell’s Theory". Air & Space Power Course. College of Aerospace Doctrine, Research and Education. 22 September 2011.
- Stephen Trimble (22 September 2011). "XCLUSIVE: US Air Force combat fleet's true operational costs revealed". Stephen Trimble's The Dew Line. Flight Global.
- Lee, Arthur Gould. No Parachute. London: Jarrolds, 1968. ISBN 0-09-086590-1.
- Eric Lawson, Jane Lawson (2002). "The First Air Campaign: August 1914– November 1918". Da Capo Press. p.123. ISBN 0-306-81213-4
- Harry Furniss (2000). "Memoirs one: the flying game". Trafford Publishing. ISBN 1-55212-513-0
- John Buckley (1998). "Air power in the age of total war". Taylor & Francis. p.43. ISBN 1-85728-589-1
- Sherman, Steven. "Aces of the Eighth Air Force in World War Two." acepilots.com, June 1999. Retrieved: 7 August 2011.
- Eden p. 370
- Ireland & Grove p. 182
- Darling, David. "Lippisch Ente", The Internet Encyclopedia of Science – Experimental Aircraft. Accessed 5 October 2008.
- "Me-163 Komet". Planes of Fame Air Museum. Accessed 5 October 2008.
- Munson, Kenneth. Fighters and Bombers of World War II. New York City: Peerage Books, 1983, p. 159. ISBN 0-907408-37-0.
- For one representation, see: Yoon, Joe. "Fighter Generations". Aerospaceweb.org. Retrieved 5 October 2008.
- Hallion, Richard P. "A Troubling Past: Air Force Fighter Acquisition since 1945." Airpower Journal, Winter 1990.
- Where Have All the Phantoms Gone? Ralph Wetterhahn Air & Space Magazine, 1 January 2009
- Duane Robert Worley (2006). Shaping U.S. military forces: revolution or relevance in a post–Cold War world. Greenwood Publishing Group. p. 125. ISBN 978-0-275-99031-2. Retrieved 20 January 2011.
- CRS RL33543, Tactical Aircraft Modernization: Issues for Congress 9 July 2009
- H.R.2647 – National Defense Authorization Act for Fiscal Year 2010
- LockMart's 5TH Generation Fighters
- Watts, Jonathan; Borger, Julian (5 January 2011). "Chinese jet fighter 'sighting' raises fears over region's military power balance". The Guardian (London).
- Chinese J-20 Logs First Flight – AviationWeek.com
- Next Generation Tactical Aircraft (Next Gen TACAIR) CRFI posted, Lucky Bogey, 12 November 2010.
- The Sixth Generation Fighter, Airforce Magazine, 2009-10.
- Hecht, Jeff. "Has China's new jet launched a stealth arms race?" New Scientist, 21 January 2011.
- "USAF wants F-22 Replacement by 2030", IDRW, Reuters.
- USAF: Next Generation Tactical Aircraft (Next Gen TACAIR) Materiel and Technology Concepts Search, USA: FBO.
- Air Force Kicks Off Search for 6th-Gen Fighter, Defense Tech, 5 November 2010.
- Trimble, Stephen (2010-5), "Boeing plots return to next-generation fighter market", The Dewline, Flight Global.
- Boeing displays manned F/A-XX concept jet, Flight Global, 9 July 2009.
- Coox, Alvin D. Nomonhan: Japan Against Russia, 1939. Two volumes; 1985, Stanford University Press. ISBN 0-8047-1160-7.
- Eden, Paul (General Editor). The Encyclopedia of Aircraft of WWII. London: Amber Books, Ltd, 2004. ISBN 1-904687-07-5.
- Ireland, Bernard and Eric Grove. Jane's War at Sea. UK: Harper Collins Publishers, 1997. ISBN 0-00-472065-2.
- Chart of fighter generations at Airforce Magazine.
- USAF posters for five generations of jet fighters.
- Fighter-planes.com: Data and images on fighter-planes.com
- Fighter aircraft Info, Articles & Pictures on fighter-planes.tk
- Fighter Aircraft News on defencetalk.com