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Aviation History
1942
1942 - 2356.PDF
522 F LI G H FIGHTER ARMAMENT nature is too often overlooked. From many points of view the 0.5m. gun is an attractive proposition for use on fighters, but it is pro bable that it will be mote widely adopted for defensive installations on bombers. The effective range of the '' half-inch '' gun is much greater than that of the 0.303m., and this fact has been utilised by Italian pilots, using 12.7 mm. Breda guns, when attacking R.A.F. bombers equipped with 0.303m. weapons. Nevertheless, it has been proved beyond any doubt that the difficulties of sight ing, and imperfections of installation, render close-range attacks imperative if real accuracy is to be attained. The rate of fire of a good 0.5m. gun is about goo rounds per minute. The desirability of '' closing in " on an enemy aircraft and of opening fire from the shortest possible range applies also to aircraft armed with 20 mm. and larger guns. These guns con stitute the fourth category under consideration. Too much has been made, not only of the long- range possibilities of aircraft "cannon," but of the destructive power of H.E. ammunition. Before the war it was commonly believed that a single hit with a 20 mm. H.E. shell would lead to the destruction-t5f'a small aircraft, such as a single-seater fighter, and that two or three strikes would account for a twin-engined bomber. It has been amply demonstrated during the war that this is far from the truth. Another popular misconception is that 20 mm. aircraft guns fire H.E. ammunition exclusively. In practice, ball, armour-piercing and in cendiary are used, particularly good results having been obtained with "A.P." It may also be explained at this point that the description " twenty millimetre " alone does not give an indication of the powers of a weapon. Nor is it sufficient to refer, say, to a " 20 mm. Oerlikon," for that concern alone makes three distinct models of 20 mm. aircraft gun; the "FF," with a muzzle velocity of about 1,800ft./sec. (this is the best-known type); the "FFL," which has a velocity of 2,250ft./sec. ; and the "FFS," which is capable of 2,490ft./sec. The muzzle velocity varies, of course, with the type of ammunition. 75 mm. Weapons The preponderance of 20 mm. over all other weapons larger than 0.5m. is apparent in the air forces of all the Powers, and it may be taken that this is the most satisfactory bore for present requirements, having regard to rate of fire, muzzle velocity and destructive power. An incidental advantage is that this calibre has also been standardised f jr light anti-aircraft and anti-tank guns. Of particular interest is the evolution of the German Mauser MG/151, one of the most efficient weapons in the category under review. This gun was first intro duced in 15 mm. calibre, and, due to the comparatively small size and weight of the projectile and the heavy propellant. charge contained in the '' bottle-neck '' cartridge, had an unusually high muzzle velocity. The rate of fire of over 700 rounds per minute was also remarkable. To-day, although the 15 mm. gun is still in service, the MG151/20, of 20 mm. N.OVEMJBER I2TB, Re-aiming 20 mm/Hispano cannons in the post" wing of a Hurricane IIC. Tk£disintegrating belts are fed J&fough the circular devices ,sh<Jwn resting on the leading edge. C9AN AMMUNITION FOR, OUTBOARD CANNON Plan view of the FW 190 A3. The two outboard weapons are 20 mm. drum-fed short Oerlikons and the two inner cannon 20 mm. belt-fed Mauser 151/20s. (Below) The gun firing switch on the top of the Me 109 control columns. The belief that this gun calibre, is much more common. is identical with the 15 mm. type except for the barrel is false. In the fourth category (guns of 37 mm. bore and over) the picture changes completely. With guns of such large A calibre it is at present impossible to attain anything ap proaching the rate of fire of a 20 mm. weapon, and thV supply of ammunition, due to considerations of weight and stowage space, must be very limited. The destructive power of the projectiles will, of course, be much greater than that of the 20 mm. size, but the idea that an aircraft will inevitably be brought down by a single hit is erroneous. This is"proved by the failure of 40 mm. antiaircraft guns to account for an enemy aircraft with every hit registered. It is likely that, in the immediate future, the 37 mm. class of gun will be employed, chiefly on specialised low- flying attack aircraft, and that its general adoption for use on fighters will depend on its technical evolution during the next year or two. Guns of appreciably larger calibre are not likely to be in general use during the next two years, though their ultimate employment is by no means unlikely, since gun- of up to 75 mm. calibre have already been installed experi mentally. To be continued'next week.)
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