World War II C.200 in the markings of 372° Sq. Regia Aeronautica

Messerschmitt Bf 109G-2/Trop 'Black 6'

The Mitsubishi A6M Zero typified the highly manoeuvrable, but lightly armored, fighter design

Aerial combat formed an important part of World War II military doctrine. The ability of aircraft to locate, harass, and interdict ground forces was an instrumental part of the German combined-arms doctrine, and their inability to achieve air superiority over Britain made a German invasion unfeasible. 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."

During the 1930s, two different streams of thought about air-to-air combat began to emerge, resulting in two different approaches to monoplane fighter development. In Japan and Italy especially, there continued to be a strong belief that lightly armed, highly maneuverable single-seat fighters would still play a primary role in air-to-air combat. Aircraft such as the Nakajima Ki-27, Nakajima Ki-43 and the Mitsubishi A6M Zero in Japan, and the Fiat G.50 and Macchi C.200 in Italy epitomized a generation of monoplanes designed to this concept. This Supermarine Spitfire XVI was typical of World War II fighters optimized for high level speeds and good climb rates

The other stream of thought, which emerged primarily in Britain, Germany, the Soviet Union, and the United States was the belief that the high speeds of modern combat aircraft and the g-forces imposed by aerial combat meant that dogfighting in the classic World War I sense would be impossible. Fighters such as the Messerschmitt Bf 109, the Supermarine Spitfire, the Yakovlev Yak-1 and the Curtiss P-40 Warhawk were all designed for high level speeds and a good rate of climb. Good maneuverability was desirable, but it was not the primary objective.

The 1939 Soviet-Japanese Battle of Khalkhyn Gol and the initial German invasion of Poland that same year were too brief to provide much feedback to the participants for further evolution of their respective fighter doctrines. During the Winter War, the greatly outnumbered Finnish Air Force, which had adopted the German finger-four formation, bloodied the noses of Russia's Red Air Force, which relied on the less effective tactic of a three-aircraft delta formation.

European theater (Western Front)

The Battle of France, however, gave the Germans ample opportunity to prove they had mastered the lessons learned from their experiences in the Spanish Civil War. The Luftwaffe, with more combat-experience pilots and the battle-tested Messerschmitt Bf 109 fighter operating in the flexible finger-four formation, proved superior to its British and French contemporaries relying on the close, three-fighter "vic" (or "V") and other formations, despite their flying fighters with comparable maneuver performance.

The Battle of Britain was the first major military campaign to be fought entirely by air forces, and it offered further lessons for both sides. Foremost was the value of radar for detecting and tracking enemy aircraft formations, which allowed quick concentration of fighters to intercept them farther from their targets. As a defensive measure, this ground-controlled interception (GCI) approach allowed the Royal Air Force (RAF) to carefully marshal its limited fighter force for maximum effectiveness. At times, the RAF's Fighter Command achieved interception rates greater than 80%.

In the summer of 1940, then Flight Lieutenant Adolph Malan introduced a variation of the German formation that he called the "fours in line astern", which spread into more general use throughout Fighter Command. In 1941, Squadron Leader Douglas Bader adopted the "finger-four" formation itself, giving it its English-language name.

The Battle of Britain also revealed inadequacies of extant tactical fighters when used for long-range strategic attacks. The twin-engined heavy fighter concept was revealed as a failed concept as the Luftwaffe's heavily armed but poorly maneuverable Messerschmitt Bf 110s proved highly vulnerable to nimble Hurricanes and Spitfires; the Bf 110s were subsequently relegated to night fighter and fighter-bomber roles for which they proved better-suited. Furthermore, the Luftwaffe's Bf 109s, operating near the limits of their range, lacked endurance for prolonged dogfighting over Britain. When bomber losses induced Reichsmarschall Hermann Göring to assign most fighters to close-in escort duties, forcing them to fly and maneuver at reduced speeds, German fighter effectiveness fell and losses rose. Long-range escort fighters like this P-51D Mustang provided protection for Allied strategic bombers

The Allies themselves, however, would not learn this latter lesson until they sustained heavy bomber losses of their own during daylight raids against Germany. Despite the early assertions of strategic bombing advocates that "the bomber will always get through", even heavily armed U.S. Army Air Force (USAAF) bombers like the Boeing B-17 Flying Fortress and Consolidated B-24 Liberator suffered such high losses to German fighters (such as the Focke-Wulf Fw 190 "bomber destroyer") and flak (AAA) that - following the second raid on Schweinfurt in August 1943 - the U.S. Eighth Air Force was forced to suspend unescorted bombing missions into Germany until longer-range fighters became available for escort. These would appear in the form of Lockheed P-38 Lightnings, Republic P-47 Thunderbolts and North American P-51 Mustangs. The use of drop tanks also became common, which further made the heavy twin-engine fighter designs redundant, as single-engine fighters could now cover a similar distance. Extra fuel was carried in lightweight aluminum tanks below the aircraft, and the tanks were discarded when empty. Such innovations allowed American fighters to range over Germany and Japan by 1944.

As the war progressed, the growing numbers of these advanced, long-range fighters flown by pilots with increasing experience eventually overwhelmed their German opposition, despite the Luftwaffe's introduction of technological innovations like jet- and rocket-powered interceptors. The steady attrition of experienced pilots forced the Germans to more frequently dip into their training pool to make up numbers when casualties surged. While new Allied airmen in Europe were well-trained, new Luftwaffe pilots were seldom able to get effective training - particularly by the summer of 1944, when Allied fighters often loitered around their airfields. Luftwaffe training flights were additionally hampered by the increasingly acute fuel shortages that began in April 1944.

European theater (Eastern Front)

On the Eastern Front, the strategic surprise of Operation Barbarossa demonstrated that Soviet air defense preparations were woefully inadequate, and the Great Purge rendered any lessons learned by the Red Air Force command from previous experience in Spain and Finland virtually useless. During the first few months of the invasion, Axis air forces were able to destroy large numbers of Red Air Force aircraft on the ground and in one-sided dogfights. However, by the winter of 1941-1942, the Red Air Force was able to put together a cohesive air defense of Moscow, successfully interdict attacks on Leningrad, and begin production of new aircraft types in the relocated semi-built factories in the Urals, Siberia, Central Asia and the Caucasus. These facilities produced more advanced monoplane fighters, such as the Yak-1, Yak-3, LaGG-3, and MiG-3, to wrest air superiority from the Luftwaffe. However, Soviet aircrew training was hasty in comparison to that provided to the Luftwaffe, so Soviet pilot losses continued to be disproportionate until a growing number of survivors were matched to more effective machines.

Beginning in 1942, significant numbers of British, and later U.S., fighter aircraft were also supplied to aid the Soviet war effort, with the Bell P-39 Airacobra proving particularly effective in the lower-altitude combat typical of the Eastern Front. Also from that time, the Eastern Front became the largest arena of fighter aircraft use in the world; fighters were used in all of the roles typical of the period, including close air support, interdiction, escort and interception roles. Some aircraft were armed with weapons as large as 45 mm cannon (particularly for attacking enemy armored vehicles), and the Germans began installing additional smaller cannons in under-wing pods to assist with ground-attack missions.

Pacific theatreGrumman F4F-3 Wildcat on patrol in early 1942

In the Pacific Theater, the experienced Japanese used their latest Mitsubishi A6M "Zero" to clear the skies of all opposition. Allied air forces - often flying obsolete aircraft, as the Japanese were not deemed as dangerous as the Germans - were caught off-guard and driven back until the Japanese became overextended. While the Japanese entered the war with a cadre of superbly trained airmen, they were never able to adequately replace their losses with pilots of the same quality, resulting in zero leave for experienced pilots and sending pilots with minimal skill into battle, while the British Commonwealth Air Training Plan and U.S. schools produced thousands of competent airmen, compared to hundred the Japanese graduated a year before the war. Japanese fighter planes were also optimized for agility and range, and in time Allied airmen developed tactics that made better use of the superior armament and protection in their Grumman F4F Wildcats and Curtiss P-40s. From mid-1942, newer Allied fighter models were faster (Wildcat was 13 mph slower than the Zero, but the Warhawk was 29 mph faster) and better-armed than the Japanese fighters. Improved tactics such as the Thach weave helped counter the more agile Zeros and Nakajima Ki-43 'Oscars'. Japanese industry was not up to the task of mass-producing fighter designs equal to the latest Western models, and Japanese fighters had been largely driven from the skies by mid-1944.

Technological innovations

Piston-engine power increased considerably during the war. The Curtiss P-36 Hawk had a 900 hp (670 kW) radial engine but was soon redesigned as the P-40 Warhawk with a 1100 hp (820 kW) in-line engine. By 1943, the latest P-40N had a 1300 hp (970 kW) Allison engine. At war's end, the German Focke-Wulf Ta 152 interceptor could achieve 2050 hp (1530 kW) with an MW-50 (methanol-water injection) supercharger and the American P-51H Mustang fitted with the Packard V-1650-9 could achieve 2218 hp (1650 kW) under war emergency power. The Spitfire Mk I of 1939 was powered by a 1030 hp (770 kW) Merlin II; its 1945 successor, the Spitfire F.Mk 21, was equipped with the 2035 hp (1520 kW) Griffon 61. Likewise, the radial engines favored for many fighters also grew from 1,100 hp (820 kW) to as much as 2090 hp (770 kW) during the same timeframe.

The first turbojet-powered fighter designs became operational in 1944, and clearly outperformed their piston-engined counterparts. New designs such as the Messerschmitt Me 262 and Gloster Meteor demonstrated the effectiveness of the new propulsion system. (Rocket-powered interceptors - most notable the Messerschmitt Me 163 - appeared at the same time, but proved less effective.) Many of these fighters could do over 660 km/h in level flight, and were fast enough in a dive that they started encountering the transonic buffeting experienced near the speed of sound; such turbulence occasionally resulted in a jet breaking up in flight due to the heavy load placed on an aircraft near the so-called "sound barrier". Dive brakes were added to jet fighters late in World War II to minimize these problems and restore control to pilots. Focke-Wulf Fw 190D-9 fighter-bomber

More powerful armament became a priority early in the war, once it became apparent that newer stressed-skin monoplane fighters could not be easily shot down with rifle-caliber machine guns. The Germans' experiences in the Spanish Civil War led them to put 20 mm cannons on their fighters. The British soon followed suit, putting cannons in the wings of their Hurricanes and Spitfires. The Americans, lacking a native cannon design, instead chose to place multiple .50 caliber (12.7 mm) machine guns on their fighters. Armaments continued to increase over the course of the war, with the German Me 262 jet having four 30 mm cannons in the nose. Cannons fired explosive shells, and could blast a hole in an enemy aircraft rather than relying on kinetic energy from a solid bullet striking a critical subsystem (fuel line, hydraulics, control cable, pilot, etc.). A debate existed over the merits of high rate-of-fire machine guns versus slower-firing, but more devastating, cannon. German Bf 110G-4 night fighter at the RAF Museum in London

With the increasing need for close air support on the battlefield, fighters were increasingly fitted with bomb racks and used as fighter-bombers. Some designs, such as the German Fw 190, proved extremely capable in this role - though the designer Kurt Tank had designed it as a pure interceptor. While carrying air-to-surface ordnance such as bombs or rockets beneath the aircraft's wing, its maneuverability is decreased because of lessened lift and increased drag, but once the ordnance is delivered (or jettisoned), the aircraft is again a fully capable fighter aircraft. By their flexible nature, fighter-bombers offer the command staff the freedom to assign a particular air group to air superiority or ground-attack missions, as need requires.

Rapid technology advances in radar, which had been invented shortly prior to World War II, would permit their being fitted to some fighters, such as the Messerschmitt Bf 110, Bristol Beaufighter, de Havilland Mosquito, Grumman F6F Hellcat and Northrop P-61 Black Widow, to enable them to locate targets at night. The Germans developed several night-fighter types as they were under constant night bombardment by RAF Bomber Command. The British, who developed the first radar-equipped night fighters in 1940-1941, lost their technical lead to the Luftwaffe. Since the radar of the era was fairly primitive and difficult to use, larger two- or three-seat aircraft with dedicated radar operators were commonly adapted to this role. See also: List of fighter aircraft of the World War II period

Post-World War II periodLavochkin La-9 'Fritz'

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 which 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 Silver Bullet fighter, but this program was also canceled by VJ Day, with 80% of the engineering work completed. See also: List of piston-engined and hybrid propulsion fighter aircraft of the post-World War II period

Rocket-powered fightersMain article: Rocket-powered aircraft The Messerschmitt Me 163 was the fastest aircraft of WWII and the only mass-produced rocket-powered fighter

The first rocket-powered aircraft was the Lippisch Ente, which made a successful maiden flight in March 1928.[2] The only pure rocket aircraft ever to be mass-produced was the Messerschmitt Me 163 in 1944, one of several German World War II projects aimed at developing rocket-powered aircraft.[3] 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.[4]

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 existing 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 to be developed into production when economics forced curtailment of most British aircraft programs in the late 1950s. Furthermore, rapid advancements in jet engine technology had rendered mixed-power aircraft designs like Saunders-Roe's SR.53 (and its SR.177 maritime variant) obsolete. The American XF-91 Thunderceptor (which was 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 fightersIt has become common in the aviation community to classify jet fighters by "generations" for historical purposes.[5] 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.

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)Main article: First generation jet fighter

The first generation of jet fighters comprises 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 impetus for the development of turbojet-powered aircraft was to obtain a decisive advantage in maximum speed. Top speeds for fighters rose steadily throughout World War II as more powerful piston engines were developed, and had begun approaching the transonic flight regime where the efficiency of piston-driven propellers drops off considerably. Messerschmitt Me 262A at the National Museum of the United States Air Force

RAF Gloster Meteor

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 combat aircraft were jet-powered.

Despite their advantages, the early jet fighters were far from perfect, particularly in the opening years of the generation. Their operational lifespans could be measured primarily in hours; the engines themselves were fragile and bulky, and power could be adjusted only slowly. 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 ejector seats and all-moving tailplanes were introduced in this period. A de Havilland Sea Vampire Mk.10 taking off from the Royal Navy aircraft carrier HMS Ocean on 3 December 1945, the first take-off and landing of a jet-powered fighter from an aircraft carrier.

The Americans were one of the first to begin using jet fighters post-war. 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 combat maximum of many piston-engined fighters. The British designed several new jets, including the iconic de Havilland Vampire which was sold to the air forces of many nations. A MiG-15 in Polish markings

Ironically, the British transferred the technology of the Rolls-Royce Nene jet engine technology to the Soviets, who soon put it to use in their advanced Mikoyan-Gurevich MiG-15 fighters which were the first to introduce swept wings in combat, an innovation first proposed by German research which allowed flying much closer to the speed of sound than straight-winged designs such as the F-80. Their 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 compared to machine guns. Nevertheless, in the first jet-versus-jet dogfight in history, which occurred during the Korean War on 8 November 1950, an F-80 (as the P-80 had been redesignated) intercepted two North Korean MiG-15s near the Yalu River and shot them down. F-86 Sabres of the Pakistan Air Force

The Americans responded by rushing their own swept-wing F-86 squadrons to battle against the MiGs which had similar trans-sonic performance. The two aircraft had different strengths, but were similar enough that the superior technology such as a radar ranging gunsight and skills of the veteran United States Air Force pilots allowed them to prevail. F9F Panther and AJ-2 Savage conducting in-flight refueling trials in 1953

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 which would be developed into the 21st century were first introduced on swept wing subsonic Demon and Cutlass naval fighters. See also: List of first generation jet 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 aluminum 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. Dassault Mirage III

Fighter designs also took advantage of new electronics technologies that made effective radars small enough to be carried 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. Republic F-105 Thunderchief

English Electric Lightning

MiG-21F interceptor

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 (like the English Electric Lightning and Mikoyan-Gurevich MiG-21F) and fighter-bombers (such as the Republic F-105 Thunderchief and the Sukhoi Su-7). 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. See also: List of second generation jet fighters

Third-generation jet fighters (early 1960s to circa 1970)Northrop F-5

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 be introduced, replacing older "steam-gauge" cockpit instrumentation. Enhancements to improve 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 jump jet.

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, 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 single multi-barrel weapon (such as the 20 mm Vulcan) to be carried and provided greater rates of fire and accuracy. Powerplant reliability increased and jet engines became "smokeless" to make it harder to visually sight aircraft at long distances. McDonnell Douglas F-4E Phantom II

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.[6]. 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. See also: List of third generation jet fighters

Fourth generation jet fighters (circa 1970 to mid-1990s)Main article: Fourth generation jet fighter

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. McDonnell Douglas F-15 Eagle

Mikoyan MiG-29 'Fulcrum' (background) and F-16 Fighting Falcon (foreground)

Sukhoi Su-27 'Flanker'

E-M characteristics were first applied to the 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 General Dynamics' (now Lockheed Martin's) F-16 Fighting Falcon.

The F-16's manoeuvrability was further enhanced by its being designed to be slightly aerodynamically unstable. 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 were 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 of which have become essential equipment. Composite materials in the form of bonded aluminum honeycomb structural elements and graphite epoxy laminate skins began to be incorporated into flight control surfaces and airframe 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. Mikoyan MiG-31 'Foxhound'

Panavia Tornado ADV

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). Dassault Mirage 2000

McDonnell Douglas F/A-18C Hornet

Most fourth-generation fighter-bombers, such as the Boeing F/A-18 Hornet and Dassault Mirage 2000, are true multirole warplanes, designed as such from the start. This was facilitated by multimode avionics which 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). Dedicated attack roles were generally assigned either to interdiction strike aircraft such as the Sukhoi Su-24 and Boeing F-15E Strike Eagle or to armored "tank-plinking" close air support (CAS) specialists like the Fairchild-Republic A-10 Thunderbolt II and Sukhoi Su-25.

Perhaps the most novel technology to be 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 to be 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 amongst 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. See also: List of fourth generation jet fighters

4.5th generation jet fighters (1990s to the present)Saab JAS-39 Gripen

Dassault Rafale

Eurofighter Typhoon

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, and research and development programs intended to produce what was then anticipated to be "fifth-generation" fighters took serious hits; many programs were canceled during the first half of the 1990s, and those which 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 have 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. Boeing F/A-18E Super Hornet

Lockheed Martin F-16E Block 60

"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, Saab JAS 39 Gripen NG and the HAL Tejas. Boeing F-15E Strike Eagle

Sukhoi Su-30MKI 'Flanker-H'

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 variant of the Cold War-era F-15 Eagle, the Sukhoi Su-30MKI which is a further development of the Su-30 fighter and the Mikoyan MiG-29M/35, an upgraded version of the 1980s MiG-29. The Su-30MKI and MiG-35 use two- and three-dimensional thrust vectoring engines respectively so as to enhance maneuvering. Most 4.5 generation aircraft are being retrofitted with Active Electronically Scanned Array (AESA) radars and other state-of-the art avionics such as electronic counter-measure systems and forward looking infrared.

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, only the Super Hornet, Strike Eagle, and the Rafale have seen combat action. Some others, such as HAL Tejas, are yet to achieve full operational clearance.[7]

The United States Government defines 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."[8][9]See also: List of 4.5 generation jet fighters

Fifth generation jet fighters (2005 to the present)Main article: Fifth generation jet fighter Lockheed Martin F-22 Raptor

Lockheed Martin F-35 Lightning II CTOL Variant

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. (Requires software upgrade on the F-22.) These sensors, along with advanced avionics, glass cockpits, helmet-mounted sights (not available 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.[10] 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 a sine qua non 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, and stealth technology.

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 very-low-observables stealth. 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, attention has also been paid to reducing IR signatures. 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).

The expense of developing such sophisticated aircraft is as high as their capabilities. The U.S. Air Force had originally planned to acquire 650 F-22s, but it now appears that only 187 will be built. As a result, its unit flyaway cost (FAC) is reported to be around $140 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 3000 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 anticipated to enter service circa 2012-2015. In October 2007, Russia and India signed an agreement for joint participation in a Fifth-Generation Fighter Aircraft Program (FGFA), which will give India responsibility for development of a two-seat model of the PAK-FA. India is also developing its own indigenous fifth generation aircraft named Medium Combat Aircraft. China is reported to be pursuing multiple fifth-generation projects under the western code name; J-XX, while Japan is exploring their technical feasibility to produce fifth-generation fighters

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