An interceptor aircraft, or simply interceptor, is a type of fighter aircraft designed specifically for the defensive interception role against an attacking enemy aircraft, particularly bombers and reconnaissance aircraft.FIREPOWER: THE WEAPONS THE PROFESSIONALS USE - AND HOW. INTERCEPTORS, #23 Orbis Publishing 1990 This role originally involved zero-notice, short missions from well-supplied ground bases against an approaching high-altitude target, necessitating readiness, climb rate, speed, maneuverability and short-range weapons capability over other factors in aircraft design. The role later evolved into a broader spectrum of missions favored by a general design emphasis around speed and climb rate. Aircraft that are capable of being or are employed as both "standard" air superiority fighters and as interceptors are sometimes known as fighter-interceptors. In the post-World War II jet age, there are two general classes of interceptor: light fighters, designed for high performance over short range; and heavy fighters, which are intended to operate over longer ranges, in contested airspace and adverse meteorological conditions. While the second type was exemplified historically by specialized night fighter and all-weather interceptor designs, the integration of mid-air refueling, satellite navigation, on-board radar, and beyond visual range (BVR) missile systems since the 1960s has allowed most frontline fighter designs to fill the roles once reserved for specialized night/all-weather fighters.
For daytime operations, conventional light fighters have normally filled the interceptor role. Day interceptors have been used in a defensive role since World War I, and are perhaps best known from major actions like the Battle of Britain, when the Supermarine Spitfire and Hawker Hurricane were part of a successful defensive strategy. However, dramatic improvements in both ground-based and airborne radar gave greater flexibility to existing fighters and few later designs were conceived as dedicated day interceptors. Exceptions include the Messerschmitt Me 163 Komet, which was the only rocket-powered, crewed military aircraft to see combat. To a lesser degree, the Mikoyan-Gurevich MiG-15, which had heavy armament specifically intended for anti-bomber missions, was also a specialized day interceptor.
Night fighters and bomber destroyers are interceptors of the heavy type, although initially they were rarely referred to as such. In the early Cold War era the combination of jet-powered bombers and nuclear weapons created air force demand for highly capable interceptors; it is in regards to this period that the term is perhaps most recognized and used. Cold War-era interceptors became increasingly distinct from their air superiority counterparts, with the former often sacrificing range, endurance, and maneuverability for speed, rate of climb, and armament dedicated to attacking large strategic bombers. Examples of classic interceptors of this era include the Convair F-106 Delta Dart, Sukhoi Su-15, and English Electric Lightning.
Through the 1960s and 1970s, the rapid improvements in design led to most air-superiority and multirole fighters, such as the Grumman F-14 Tomcat and McDonnell Douglas F-15 Eagle, having the performance to take on the point defense interception role, and the strategic threat moved from bombers to intercontinental ballistic missiles (ICBMs). Dedicated interceptor designs became increasingly rare, with the only widely used examples designed after the 1960s being the Panavia Tornado ADV, Mikoyan MiG-25, Mikoyan MiG-31, and the Shenyang J-8.
History
The first interceptor squadrons were formed during World War I to defend London against attacks by Zeppelins and later against fixed-wing long-range bombers. Early units generally used aircraft withdrawn from front-line service, notably the Sopwith Pup. They were told about their target's location before take-off from a command centre in the Horse Guards building. The Pup proved to have too low performance to easily intercept Gotha G.IV bombers, and the superior Sopwith Camels supplanted them.
The term "interceptor" was in use by 1929.The Gloster S.S.8, Flight, 6 December 1929, Page 1273: "the type of single-seater fighter known as an "Interceptor" is a class of aircraft designed, as the title suggests, for intercepting hostile aircraft." Through the 1930s, bomber aircraft speeds increased so much that conventional interceptor tactics appeared impossible. Visual and acoustic detection from the ground had a range of only a few miles, which meant that an interceptor would have insufficient time to climb to altitude before the bombers reached their targets. Standing combat air patrols were possible but only at great cost. The conclusion at the time was that "the bomber will always get through".
The invention of radar made possible early, long-range detection of aircraft on the order of , both day and night and in all weather. A typical bomber might take twenty minutes to cross the detection zone of early radar systems, time enough for interceptor fighters to start up, climb to altitude and engage the bombers. Ground controlled interception required constant contact between the interceptor and the ground until the bombers became visible to the pilots and nationwide networks like the Dowding system were built in the late 1930s to coordinate these efforts.
During World War II the effectiveness of interceptor aircraft meant that bombers often needed to be escorted by long range fighter aircraft. Many aircraft were able to be fitted with Aircraft interception radar, further facilitating the interception of enemy aircraft.
The introduction of jet power increased flight speeds from around to around in a step and roughly doubled operational altitudes. Although radars also improved in performance, the gap between offense and defense was dramatically reduced. Large attacks could so confuse the defense's ability to communicate with pilots that the classic method of manual ground controlled interception was increasingly seen as inadequate. In the United States, this led to the introduction of the Semi-Automatic Ground Environment to computerize this task, while in the UK it led to enormously powerful radars to improve detection time.The introduction of the first useful surface to air missiles in the 1950s obviated the need for fast reaction time interceptors as the missile could launch almost instantly. Air forces increasingly turned to much larger interceptor designs, with enough fuel for longer endurance, leaving the point-defense role to the missiles. This led to the abandonment of a number of short-range designs like the Avro Arrow and Convair F-102 in favor of much larger and longer-ranged designs like the North American F-108 and MiG-25.
In the 1950s and 1960s during the Cold War, a strong interceptor force was crucial for the opposing superpowers as it was the best means to defend against an unexpected nuclear attack by strategic bombers. Hence, for a brief period of time they fared rapid development in both speed, range, and altitude. At the end of the 1960s, a nuclear attack became unstoppable with the introduction of ballistic missiles capable of approaching from outside the atmosphere at speeds as high as . The doctrine of mutually assured destruction replaced the trend of defense strengthening, making interceptors less strategically logical. The utility of interceptors waned as the role merged with that of the heavy air superiority fighter.
The interceptor mission is, by its nature, a difficult one. Consider the desire to protect a single target from attack by long-range bombers. The bombers have the advantage of being able to select the parameters of the mission – attack vector, speed and altitude. This results in an enormous area from which the attack can originate. In the time it takes for the bombers to cross the distance from first detection to being on their targets, the interceptor must be able to start, take off, climb to altitude, maneuver for attack and then attack the bomber.
A dedicated interceptor aircraft sacrifices the capabilities of the air superiority fighter and multirole fighter (i.e., countering enemy fighter aircraft in air combat manoeuvring), by tuning its performance for either fast climbs or high speeds. The result is that interceptors often look very impressive on paper, typically outrunning, outclimbing and outgunning slower fighter designs. However, pure interceptors fare poorly in fighter-to-fighter combat against the same "less capable" designs due to limited maneuverability especially at low altitudes and speeds.
Point-defense interceptors
In the spectrum of various interceptors, one design approach especially shows sacrifices necessary to achieve decisive benefit in a chosen aspect of performance. A "point defense interceptor" is of a lightweight design, intended to spend most of its time on the ground located at the defended target, and able to launch on demand, climb to altitude, manoeuvre and then attack the bomber in a very short time, before the bomber can deploy its weapons.
At the end of Second World War, the Luftwaffes most critical requirement was for interceptors as the Commonwealth and American air forces pounded German targets night and day. As the bombing effort grew, notably in early 1944, the Luftwaffe introduced a rocket-powered design, the Messerschmitt Me 163 Komet, in the very-short-range interceptor role. The engine allowed about 7 minutes of powered flight, but offered such tremendous performance that they could fly right by the defending fighters. The Me 163 required an airbase, however, which were soon under constant attack. Following the Emergency Fighter Program, the Germans developed even odder designs, such as the Bachem Ba 349 Natter, which launched vertically and thus eliminated the need for an airbase. In general all these initial German designs proved difficult to operate, often becoming death traps for their pilots, and had little effect on the bombing raids. Rocket-boosted variants of both of Germany's jet fighters; the Me 262 in its "C" subtype series, all nicknamed "home protector" (Heimatschützer, in four differing formats) and the planned He 162E subtype, using one of the same BMW 003R turbojet/rocket "mixed-power" engine as the Me 262C-2b Heimatschützer II, but were never produced in quantity.
In the initial stage of Cold War, bombers were expected to attack flying higher and faster, even at transonic speeds. Initial transonic and supersonic fighters had modest internal fuel tanks in their slim fuselages, but a very high fuel consumption. This led fighter prototypes emphasizing acceleration and operational ceiling, with a sacrifice on the loiter time, essentially limiting them to point defense role. Such were the mixed jet/rocket power Republic XF-91 or Saunders Roe SR.53. The Soviet and Western trials with zero-length launch were also related. None of these found practical use. Designs that depended solely on jet engines achieved more success with the F-104 Starfighter (initial A version) and the English Electric Lightning.