A fighter aircraft is a fast and maneuverable aircraft, whose capabilities include attacking other aircraft. There are a variety of missions, and many fighters are best at one but can do others. A few multirole fighters truly do all jobs well, although a specialized aircrat may be superior for a specific mission.
Jet-propelled fighters are classed in "generations".
Within a given generation, there may be specific fighters optimized for a particular mission.
Air superiority fighter
Optimized for engaging and destroying other fighter aircraft, often at long range. While it was limited to gun range, the F-86 Sabre was one such aircraft, while the F-15 Eagle is an advanced air superiority fighter, allegedly developed with the motto "not a pound for air to ground" (see F-15E Strike Eagle)
Interceptors may be short- or long-range. Short-ranged interceptors, such as the MiG-21, protect relatively small areas. Long-range interceptors, such as the MiG-25 or F-102 often are optimized for destroying enemy bombers far from their target. Interceptors are purely defensive (i.e., defensive counter-air), while air superiority fighters can be offensive or defensive.
This type is optimized for attacking ground targets. Depending on the specific type, it may have relatively more or less ability to engage in air-to-air combat. Some aircraft designated as "fighters" have no air-to-air capability, such as the F-117 Nighthawk, which is really a light bomber. Other fighter-bombers, such as the F-105, do have some air combat capability, but generally would concentrate on the attack mission, perhaps relying on speed to avoid interceptors.
While almost all fighters have, at one time, been used in both ground attack and air-to-air combat, a true multirole fighter does both well. Historically, when a reasonably versatile fighter-bomber such as the F-4 Phantom II met other fighters, it jettisoned its bombload to gain maneuvering performance. Forcing the aircraft to jettison its bombs far from the target defeated its primary mission.
More recent aircraft, however, have demonstrated true multirole capability. In 1991, during Operation Desert Storm, U.S. Navy F-18 Hornet aircraft, assigned to attack a ground target, were intercepted by Iraqi fighters. Without jettisoning their bombload, the Hornets shot down the other aircraft, and completed their attack mission. The F-15E Strike Eagle also can perform at this level.
The idea of a fighter generation is useful only for approximate comparison of fighters.
The first generation of jet fighters were subsonic, armed with machine guns or autocannon for air-to-air combat, and had limited electronics. While there were earlier models, such as the Second World War German Me-262, U.S. F-80 Shooting Star and British Meteor, the most common examples are the Korean War-vintage U.S. F-86 Sabre and Soviet Mig-15/NATO reporting name FAGOT.
Typified by the Soviet MiG-17/NATO reporting name FRESCO and U.S. F-100 Super Sabre, these were the first supersonic fighters, typically with limited onboard radar, and both guns and early air-to-air missiles (e.g., AIM-9 Sidewinder).
In this generation were the first serious attempts at multirole capability, such as the F-4 Phantom II, originally developed by the U.S. Navy but operated by a large number of countries. An early Soviet design with multirole capability was the MiG-23/NATO reporting name FLOGGER.
Fighters of this vintage had major advances in electronics and missiles. While each previous generation had been faster than the one before it, fourth generation fighters emphasized maneuverability, missiles that could attack from any angle, and long range. Soviet fighters of this generation include the Su-27 /NATO reporting name FLANKER and MiG-29/NATO reporting name FULCRUM. U.S. equivalents split into "high-end" and "low-end", the high end, such as the F-15 Eagle initially optimized for air superiority, and the low-end, such as the F-16 Fighting Falcon, as multirole.
Some of these aircraft have significant improvements in the human interface between crew and systems. For example, a technique called Hands On Throttle And Stick (HOTAS) puts all critical controls (e.g., the weapons release switches) onto side-mounted control stick and throttle, so a pilot doing violent maneuvering under heavy gravitational mode need not ever struggle to reach a separate switch.
Heads-up displays (HUD) also became more dominant, so the pilot could concentrate on things outside the aircraft, with critical information (e.g., available weapons, alarms, etc.) were superimposed on his normal vision.
HOTAS and HUD add considerable learning time to master the aircraft. The limited space for buttons and other controls on the two sticks sometimes means that pairs of buttons (i.e., "chording") need to be pushed simultaneously to give a certain second-priority command to the aircraft. Aircrew speak of having to master "switchology" to make these hand movements reflexive. Learning not to be overloaded by the additional information in a HUD takes training and practice.
Several aircraft have significantly advanced electronics, maneuverability, or other features when compared to the basic fourth generation. The human interface between the crew and the user has additional features that improve situational awareness. For example, rather than dozens or hundreds of specialized displays, the typical cockpit has two or four large displays, onto which the crewmember can select what is most important at that time. On the way to a target, displays might be showing navigation, air defense threats, status of one's own weapons, and perhaps general engine performance. When actually making an attack run, the navigation display might change to a detailed target display; the weapons display changes to the programming of the specific precision-guided munition to be used; the engine display changes to an enlarged view of air defences. On exiting the target, there might be a wide-angle view of threats on the return path.
While these are not new to generation 4.5, controls and displays much more coupled to the user have advanced. For example, while Hands on Throttle and Stick and heads-up display existed in the fourth generation, there are now things variously called helmet cueing or eye movement tracking: without having to move one's hands, the pilot can look at a target and his weapons and sensors follow his vision to lock onto a target.
Aircraft of the current generation are more revolutionary than evolutionary, the example most often cited being the U.S. F-22 Raptor. They have low observability (i.e., stealth), supercruise, extremely advanced avionics including extremely flexible AESA radars low probability of intercept, and may have supercruise, the ability to fly at supersonic speed without an afterburner.
While it is not stealthy and does not have supercruise, the F-18 Super Hornet, especially the Block 30/Super Hornet II+ has avionics comparable to the F-22
The U.S. F-35 Joint Strike Fighter does not have supercruise, but is better at ground attack than the F-22, and also has short-takeoff versions. Russian technology here is emerging, but the Su-47 may be of this generation.