Modern Western Weapons

There was a period in the 1950s and 1960s when most nations felt that guns would no longer be required, and several fighters were designed to use only missiles. Most of these, such as the USAFs F-102A and F-106A, were intended for intercepting strategic bombers. Naval fighters such as the RNs Sea Vixen and the USNs F-4 Phantom II were also introduced without guns.

The US realised its mistake in the Vietnam War and accordingly fitted the USAF s F-4E with an M61A1 cannon. This version achieved half of its kills with the gun rather than its missiles. Some F-106As were also modified to carry an M61A1 in the missile bay. Where guns could not be retrofitted, gun pods were used as an expedient, but they were not as rigid (and therefore as accurate) as internal cannon, besides increasing aerodynamic drag.

The experience of the Americans, Europeans and Russians in developing their current range of aircraft cannon has been markedly different. After an attempt at updating the M-39 (the Ford Tigerclaws, intended for the abortive F-20 Tigershark) the Americans have remained true to the rotary cannon. This is despite the development of an impressive twin-barrel 25mm gun, the GE 225. This chambers the NATO 25 x 137 cartridge and while using the Gast-type alternating fire principle, was tried in two versions: gas-operated (to achieve 2,000 rpm) and externally driven (variable rate up to 750 rpm).

The Americans at one time attempted to produce an advanced 25mm rotary cannon (the Philco-Ford GAU-7/A being the chosen version) intended for the F-15 fighter. The projectile was buried within a cylindrical combustible case which resembled an oversized shotgun cartridge. This was defeated by technical problems and the 20mm M61A1 has remained in US service ever since. Now produced by General Dynamics, it has even been selected for the new F-22 fighter, albeit in an improved M61A2 version, with a 480-round magazine. Ammunition performance has been improved by the adoption of the PGU-28 series, which combines a chemical fuze with a different shape to reduce aerodynamic drag by 33%.

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Gau Helical Magazine

39.7 in

Installation of 30mm GAU-8IA with magazine. The entire installation is over six metres long and the ammunition drum is one metre in diameter (Courtesy: General Electric!Ian Hogg)

A 25mm cannon is seeing US airborne service, but with the Marines, in the five-barrel GAU-12/U rotary cannon fitted externally to the AV-8B (American Harrier). This uses the conventional 25 x 137 NATO cartridge, is powered by a pneumatic drive using gas bled from the engine and has a 300-round magazine (in the form of a linear linkless feed rather than the usual helical drum, to keep down the frontal area).

Two larger guns have seen USAF service, but only in the ground-attack role. These are the massive seven-barrel General Electric GAU-8/A rotary cannon fitted to the Fairchild A-10 'tankbuster' (which was designed around the gun) and a four-barrel version of the same gun, the GAU-13/A. The 30 x 173 cartridge used by both is dimensionally identical to that of the Oerlikon KCA but uses a light-alloy instead of steel case. The GAU-8/A weighs 281kg, but the complete installation with a full magazine of 1,350 rounds crunches the scales at 1,828kg. The GAU-13/A is only available in the GPU-5A gun pod, for fitting to aircraft with only an occasional need for such firepower. It uses a pneumatic drive via a storage bottle and the pod weighs 862kg including 353 rounds of ammunition. In this case the helical magazine is arranged to store the ammunition points-forwards rather than points inwards, again to minimise liontal area. GSh-23 in TU-22M (Courtesy: Russian Aviation Research Trust)

In contrast, Western Europe has remained wedded to the revolver. In addition to the Aden, DEFA and Oerlikon developments, Mauser re-entered the market with the BK 27, a 100kg weapon capable of 120kg but can achieve a remarkable 2,500 rpm.

Mauser Cannon

firing its 27 X145B cartridges at 1,700 rpm.

However, technical problems have led to many

Introduced in the Panavia Tornado and the Alpha changes in the detailed specification of the gun and Jet light strike aircraft in the early 1970s, it has been ammunition, which at the time of writing were still selected for the SAAB Gripen (as the m/85). Although early reports indicated that a new 27mm continuing.

The British rather surprisingly decided to devel-

rotary cannon was to be developed for the op a new weapon, the Aden 25, to equip the latest

EFA2000 'Eurofighter\ it will actually be equipped marks of Harrier, instead of staying with the very with a version of the BK 27, modified for a linkless similar BK 27 which was already in RAF service feed. and seems likely to be selected for the American

The French have been primarily concerned with Joint Strike Fighter, in which Britain has a close the low muzzle velocity of their 30mm cannon, interest. The Aden is essentially similar to the earli-

which they have remedied by developing a longer er models but is designed to use the standard 25 x case (which also differs slightly in other dimension- 137 NATO round, which it fires at up to 1,850 rpm.

al details) to create the 30 x 150B. The associated Like the 30M791, it experienced considerable devel-

GIAT 30M791 cannon, intended to be fitted to the opment problems which eventually led to its cancel-

Dassault Rafale, is heavier than earlier models at lation in 1999.

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