After the Second World War there was a lull in the previously rapid development of new weapons while the Allies absorbed the progress made by German weapon designers, debated the role of aircraft guns in the light of the prospect of guided missiles and (in the case of all except the USA) struggled to recover from the disastrous financial consequences of six years of war. The post-war period can therefore be divided into phases. Until the mid-1950s, weapons based on the wartime guns remained in service (with the Korean War of 1950-53 adding some useful experience), while the slow development of the new concepts of revolver and rotary cannon took place in parallel (and in rivalry) with that of guided missiles. By the late 1950s, the 'missile school* was in the ascendant, and it was not until experience of the Vietnam War in the late 1960s confirmed the value of an integral gun that the continued place of such a weapon was assured.
This did not prevent some unusual experimental work. One British line of investigation was into the Luftwaffe s use of large airborne cannon to subject Allied bombers to artillery fire. It was felt that the use of VT (proximity) fuzes, not available to the Luftwaffe, would make this an interesting proposition and a 1947 feasibility study was therefore launched into fitting a suitably modified version of the army s 3.7" AA gun into the long-suffering de Havilland Mosquito. An idea of the implications of this can be gained from the following statistics: the army gun fired a 12.7kg shell at 800 m/s, the barrel and breech alone weighed 1,770kg and measured 4.9m, and the air service version was to be fitted with a Galliot muzzle brake which was 1.22m long, 610mm in diameter and weighed 118kg!
A slightly saner if still mind-boggling scheme was to fit a 4.50" (114mm) recoilless gun (RCL) to fighter aircraft (the Gloster Javelin was a possible host). It was to be fitted with a seven-round rotary magazine and due to the usual lightweight construction possible with RCLs was to weigh 'only* 650kg. This idea was overtaken by the prospect of the guided air-to-air missile.
To return to service weapons, the British, Americans and French fitted versions of the HS 404 to many of their early jets, with the Americans also using the .50" Browning in fighters and for bomber defence (a quad tail mounting being fitted to the B52C to G models). The Browning is still in use today, mainly in gun pods but it is currently offered mounted in the wings of the Embraer EMB-314 Super Tucano. The French even continued the use of the Mauser MG 151, initially as an AA gun but later as a helicopter weapon, and it remained in service in that guise until the 1970s.
The Americans were reluctant to give up the well-tried .50" Browning, standardised in April 1945 in the M3 version, which achieved a remarkable 1,200 rpm. Versions of the 20mm Hispano did, however, increasingly find their way into American aircraft, initially USN and later USAF fighters, until the new generation of American weapons was ready. This was prompted by battle experience in the Korean War when it was discovered that Sabre pilots were having to fire an average of 1,000 .50" calibre rounds to shoot down each enemy aircraft. The USN used the M3 version of the Hispano, uprated to 750 rpm, in the F2H-1, F9F-2 and F9F-6. The armament was probably the best compromise in Korea between rate of fire and destructive effect, but these older aircraft were not as good as the USAFs Sabre (or, more crucially, the MiG-15). The 20mm M3 was also used in the FJ-2 Fury from January 1954.
From the late 1940s the USAF used the 20mm M24, which was essentially the same as the M3 except for its electric ignition (which meant that it required different ammunition, although this confusingly retained the same M90 series designations). The M24 saw service in some versions of the F-86 and F-89 and also for bomber defence (B-36B, B-47E, B-52B), before being replaced in service by the M39 and M61. The B-36 was one of the most
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heavily defended aircraft ever to see service, mounting no fewer than sixteen M24 cannon in twin turrets.
The HS 404 design was ultimately developed into the USN's Mk 12. The origin of this weapon was for a wartime fast-firing (1,000 rpm) AA gun to counter kamikaze attacks, but it was cancelled at the end of the war. Work recommenced in 1948, initially for the electrically-primed 20 x 110 M24 cartridge, then modified for the new 20 x 102, before finally being modified again to take the navy's powerful new 20 x 110 (Mk 100 series) cartridge.
The Mk 12 was fitted to a number of aircraft including later models of the North American FJ-1 Fury, the Douglas F4D Skyray and A4D Skyhawk, the McDonnell F3H Demon and the Vought F8U Crusader. It saw considerable action in the Crusader during the Vietnam War but proved inaccurate and unreliable, persuading the USN to adopt the air force's M61 in future aircraft. The reliability problem was caused by the feed from the ammunition cans, which were located directly behind the cockpit. From there, flexible chutes guided the belts a considerable distance down to the guns. In violent manoeuvres, the chutes would flex, causing the belts to jam and pull apart.
Development of the basic HS 404 design was continued by the parent company, Hispano-Suiza, but mainly for army and naval AA guns. Some unsuccessful attempts were, however, made to produce larger-calibre aircraft cannon. Following abortive wartime experiments by BMARCO (the British Hispano subsidiary) with a 30mm aircraft cannon using a necked-up 25mm Hotchkiss case, in the early 1950s Hispano themselves competed with Aden for the Fleet Air Arm contract with the HS 825. This used a unique bottleneck 30X136 cartridge combining a relatively light shell with a high muzzle velocity (ideal for air combat) but the type of linear mechanism chosen suffered insoluble technical problems in trying to compete with the Aden's rate of fire - it was designed to reach 950-1,OOOrpm. Hispano persevered with this gun and eventually succeeded in having it selected for service in the Swiss FFA P-16 fighter-bomber. However, production of the aircraft was cancelled following several accidents.
A much longer life has been achieved by developments of the Mauser MG 213C revolver cannon, largely achieved with the aid of engineers who formerly worked for Mauser. As already described in Chapter 2, this wartime German design was developed in Britain (where Werner Jungerman worked for Aden), France (Anton Politzer worked on DEFA designs between 1947 and 1967), Switzerland (Fredrick Linder worked for Oerlikon) and the USA (Otto von Lossnitzer). The high-velocity 20mm version of the Mauser gun was intended by the Luftwaffe for two roles: bomber defence and ground attack. The low-velocity 30mm MK 213/30 was planned for fighters, to replace the MK 108.
In Europe, the 30mm version was the preferred basis for development post-war, the RAF as ever concerned with destroying heavy bombers. At first, the original MK 213/30 case length of about 85mm was used, with some modifications to the rim; this Aden 3M (Armament Development Enfield) cartridge briefly saw British service, and was subsequently referred to as the low-velocity* (LV) round. The French adopted a longer 97mm case in the DEFA 541 series to achieve a higher muzzle velocity for their Vautour and Mystère IV installations of 1954/5.
In the mid-1950s, Britain and France agreed on common chamber dimensions for the Aden Mk 4 and DEFA 550 series guns. The 30 x 113B, which has now become standard, is also used in various American cannon. The 30M552 DEFA (and the very similar -553) was used in such aircraft as the Super Mystère, Mirage III and Fl, Etendard. Jaguar and Alpha Jet, and has been built in South Africa as the 55C5, which incorporates modifications to increase the rate of fire from 1,300 to 1,800 rpm. The Aden was the standard British fighter gun from the late 1950s up to the introduction of the Mauser BK 27 in the Panavia Tornado over twenty years later (with some use of the American M61A1 in Phantom aircraft). Introduced in the Hawker Hunter it saw service in the Gloster Javelin, Supermarine Swift and Scimitar, Folland Gnat and English Electric Lightning, as well as the Saab Draken, the Commonwealth CA-27 (Avon Sabre) and HAL Marut, and is still in service in versions of the Harrier, Hawk and Jaguar.
The guns required relatively little modification
through all these cartridge changes, as the overall length of all the cartridges remained the same at 200mm. It is worth noting that the straight case design means that case length is not particularly critical, and the 30X113B cases often measure around 111mm. The guns fired at about 1,200-1,400 rpm, although the final development of the French series, the 30-554 GIAT used in the Mirage 2000, can achieve 1,800 rpm. Despite the identical appearance, ammunition for weapons of different nationalities is not necessarily interchangeable as it can vary in the gas pressure generated and the voltage required by the electric ignition system. Furthermore, British and French ammunition belts, although superficially almost identical, differ in link strength and belt flexibility. Barrel lengths also vary, affecting muzzle velocities.
Oerlikon took a different route developing their range of revolver cannon, altering the basic design more than the British and French. After offering various models without any sales they eventually achieved success in 1970 with the massive KCA, designed around an extremely powerful 30 x 173 cartridge. This outclasses the Aden/DEFA in muzzle velocity and hitting power while still achieving 1,350 rpm, but its size is such that it has only been fitted as standard to one aircraft, the SAAB Viggen (in Swedish service the KCA is known as the m/1975). It can also be installed in the Hughes Model 34 gun pod, which weighs 475kg including 125 rounds of ammunition. The KCA was considered in the USA as a fall-back in case of the GAU-8/A rotary s failure, which uses an alloy-cased and percussion-primed version of the same cartridge; known as the GAU-9/A, two would have been fitted to the A-10 aircraft. It was also planned to fit two of these guns to the Taiwanese AIDC A-3 single-seat attack version of their AT-3 trainer, but this did not progress beyond prototype status. If the aircraft had reached production, it would
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have carried one of the heaviest gun armaments of modern times.
In America, work took place on rotary as well as revolver designs but generally in smaller calibres. Most of the new guns were designed around the .60" (15.2X114) T17 anti-tank gun cartridge (which never actually saw service), its necked-out, electrically primed 20 x 102 variant, or the lengthened navy Mk 100 (20 x 110). However, there were various fruitless experiments with 30mm revolver cannon, culminating in the T182 gun whose cartridge had a lengthened version of the Aden/DEFA case (30 x 126B) for improved performance, and in the remarkable front-loading T168 described in Chapter 2.
The 20 X102 cartridge (known as the M50 series) was introduced into service in the Pontiac M39 revolver cannon, which was capable of 1,700 rpm. A few F-86F-2s Sabres, experimentally fitted with four 20mm T-160 cannon (the prototype of the M39), arrived in Korea in 1953, in time to be tested in action. Results were promising, but airframe stress and other unreliability problems meant that some years of continuing development were required before the gun was considered entirely satisfactory. It saw widespread service in the F-86H, F-100, F-101, B-57B and latterly in the Northrop F-5 series.
The Navy's Mk 11 gun, which used the Mk 100 series cartridge, was a twin-barrelled revolver cannon with a rate of fire of up to 4,200 rpm, whose only application was in the Mk 4 gun pod. The USA experimented with even larger 20mm cartridges for the T33 series of aircraft guns, achieving a muzzle velocity of 1,150 m/s, but these were not adopted.
These revolver weapons were completely overshadowed by the six-barrel General Electric M61 rotary cannon, which emerged in 1957 from 'Project Vulcan' (which basically started from the nineteenth-century Gatling gun with an electric motor attached). This rapidly became the classic
20mm GAU-4 in the SUU23A gun pod; the only service version of the 20mm Vulcan family to he gas-operated
American fighter gun of the second half of the twentieth century. It was originally belt-fed, which limited its maximum rate of fire to 4,000 rpm, but in 1964 the M61A1 was introduced, with various improvements including a linkless feed system which permitted a reliable 6,000 rpm to be achieved. Ammunition is the same 20 x 102 as the M39. Despite its ubiquity, there are drawbacks: the appetite for ammunition requires a large magazine and both magazine and gun are very bulky, the latter having a diameter of 34cm.
The M61 was first fitted to the F-104 Starfighter, and also equipped the F-105, F-106, F-4, F-l 11, F-14, F-l5, F-l6, F/A-18, A-7, the Italian AMX and (for rear defence) the B-52H and B-58 bombers. The first use of the M61A1 version was in the F-105D. The drum magazines used for the linkless feed are power-driven with the capacity varying according to the installation. The F/A-18 drum is 53cm long and 57cm in diameter and contains 570 rounds. To the gun weight of 114kg is added the drum and feed system weight of 122kg, while a full load of ammunition adds a further 145kg, giving a grand total of 381kg. This is considered to be the 'compact* version. At the other extreme was the F-111 installation, housing 2,084 rounds, which had a total weight of 790kg. The rear installation in the 20mm M61A1 in F-l 6 aircraft (Courtesy: Oeriikon-Contraves)
B52H used a sophisticated radar system with track-while-scan capabilities.
The major nations were not the only ones to design new aircraft cannon. Despite making some use of the HS 404 (known as the m/41) and HS 804 (m/47), Sweden also used Bofors weapons for their initial post-war generations of aircraft. These short-recoil guns, the m/45 and a modified version, the m/49, were designed around the Hispano s 20 x 110 ammunition and were fitted to most versions of the SAAB 21 and early jets, until replaced by the 30mm Aden (m/55) in later versions of the A32 Lansen.
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