TANKBUSTERS: AIRBORNE ANTI-TANK GUNS IN WWII
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© Anthony G Williams
This summary is based on material from 'Flying Guns: World War 2' by Emmanuel Gustin and Anthony G Williams
Amended 24 June 2004
The advent of highly mobile tank warfare at the start of World War 2 prompted a search for ways of destroying tanks from the air, with variable success. There was a preference in some quarters for using fighter-bombers armed with rockets or bombs, but while these were effective in general ground attack, including disrupting supplies to armoured units, they proved largely ineffective in directly knocking out tanks for the reasons spelled out in 'Flying Guns: WW2':
" The ineffectiveness of air attack against tanks should have caused no surprise because the weapons available to the fighter-bombers were not suitable for destroying them. Put simply, the heavy machine guns and 20 mm cannon were capable of hitting the tanks easily enough, but insufficiently powerful to damage them, except occasionally by chance. The RPs and bombs used were certainly capable of destroying the tanks but were too inaccurate to hit them, except occasionally by chance."
Experience showed that the best way of knocking out tanks was to use a cannon powerful enough to penetrate the armour. This article examines the weapons used and takes a retrospective look at an 'ideal' airborne anti-tank armament.
"The Gun Carriers: what of the aircraft?"
There were various possible locations for heavy cannon, but they all boiled down to two basic types - wing or fuselage mountings. Wing mountings had several disadvantages. First, they suffered the usual problems with this location of harmonisation; that is, the guns had to be angled inwards to coincide with the sight line, and this could only be for a specified distance. At much shorter or longer distances, the projectiles would not strike where the sights were aimed. Incidentally, it is worth mentioning that with all guns, wherever mounted, there was also a vertical harmonisation issue, in that projectiles followed a curved trajectory so at much shorter or longer distances they would strike above or below the aiming point. However, this would be much less of a problem with a high muzzle velocity. Other disadvantages of wing mounting peculiar to heavy cannon were, obviously, that the weight and drag penalties were much greater than with one fuselage-mounted gun, the wings were more flexible not just in flight but also under recoil (which affected accuracy) and the plane could be moved from side-to-side by the recoil if the guns fired at different instants, further affecting accuracy. The guns were also mounted under the plane's centre of gravity, which meant that recoil pushed the nose down on firing.
All of this added up to less accuracy and lower aircraft performance with wing-mounted cannon. This is significant because most single-engined aircraft fitted with large cannon had no option but to fit them under the wings, as few vee-engines, and no radials, were compatible with the engine-mounting of the gun. In theory, a gun could be mounted under the belly of the plane and synchronised to fire through the propeller disk, but in practice this became more problematic as the size of the cartridge case increased because of the variations in the burning time of the propellant (the Luftwaffe considered but rejected such an installation of the MK 103 in the Fw 190 for this reason).
Of course, none of these problems bothered twin-engined aircraft, which were able to employ a rigid central mounting in or under the fuselage, directly under the sights, to the great benefit of accuracy. They also usually had a much better forwards and downwards view (important for a ground attack plane), although blocked to the side by the engines. However, most twins were much bigger than singles, making them much bigger targets for ground fire. Attempts to use Ju 88s in the anti-tank role led to catastrophic loss rates. The only exception was the Hs 129, a very compact plane. However, while that was probably the most effective of all the anti-tank aircraft, it had a low performance and was relatively helpless against enemy fighters, not even having the benefit of a rear gunner.
.... Wing area is an indicator of apparent size, and therefore the risk of being hit by ground fire (although for a given wing area, twin-engined planes usually presented a bigger target). Wing loading is a double-edged sword: a low wing loading was useful for a good short-field performance and low-speed manoeuvrability, but a smaller wing was less disturbed by low-level air turbulence and therefore (other things being equal) was likely to provide a more stable gun platform for ground attack. The power loading (as with the wing loading, taken at maximum loaded weight) gives an indicator of performance. ...
Link to the full article -- Tankbuster Aircraft of WWII