The prolific Aimo Lahti also achieved some sue- War experience soon justified the concerns cess in Finland with the L-34 boat gun, a 20mm of both the British and the Americans about the .5"
cannon which used his own 20 X 113 cartridge. Not machine guns lack of range and hitting power, much information about this has survived, but it is Their high rate of fire meant that they had some known to have been recoil-operated and fired at 350 effect against strafing aircraft which came too close, rpm from either a fifteen-round box or forty-five-round drum. In Sweden, the Vickers-Terni 25mm, firing a 25 X 87R cartridge, was produced as the 125mm kulspruta Ml1922' and fitted to some submarines. The Bofors 25mm was also used.
The smallest calibre to prove its worth was the 20mm. In Allied navies, this calibre became virtually synonymous with the Oerlikon S, the most powerful of a family of API blowback 20mm weapons developed by the Swiss firm between the wars. It
IV A VAL GUIS S
was introduced by the RN in 1939 and by the USN in 1941.
Performance was only average, the 20 X 110RB cartridge being fired at a rate of about 450 rpm - no better than the significantly more powerful German 2cm FlaK 38. The cartridges normally had to be greased to ensure reliable extraction of the fired cases, although during the war a fluted chamber was introduced in the American Mk 4/4. This worked with brass cartridge cases, but the alternative steel cases still required greasing.
The sixty-round ammunition drum allowed only 7.5 seconds' firing before reloading, but the air-cooled barrel limited the continuous rate of fire in any case. While the gun had a theoretical maximum range of 4.4km, the practical maximum was only about 1.5km. However, its advantages were great simplicity, ruggedness and reliability. Most mountings had no power requirements and could be sited wherever there was space.
The most common mounting in British service was the Mk II single, which weighed between 500kg and 750kg. The hydraulically powered Mk V twin weighed 1,200kg, but later manual twin mountings weighed less than 600kg. A complex, four-bar- defensively equipped merchant ships (DEMS). The relied, belt-fed mount was developed but not RAFs 20mm Hispano cannon (HS 404) saw limit-adopted. The Oerlikon was always best suited to the ed use. Its superior performance in terms of muzzle simple manual mount, as was emphasised by the velocity, rate of fire and lighter weight did not corn-later conversion of Mk V mounting to take a single pensate for its relative fragility. Incidentally, the US
( early type) (John Lambert)
Bofors gun instead.
American mountings were generally similar to 404 in the 1970s as the Mk 16, fitted to a simple the British but they did introduce a powered manual mounting and complete with a recoil-oper-
quadruple mount, albeit still with drum-fed guns. Although it lost favour towards the end of the war.
ated chamber lubricator to avoid the need to pre-lubricate the ammunition. It should be noted that as the small shell was inadequate in dealing with although the 20 X 110 Hispano cartridges were kamikaze attacks, the Oerlikon was still immensely about the same size as those used in the Oerlikon, popular. At the end of the war the British and they were not interchangeable. The Kriegsmarine Commonwealth navies alone had about 55,000 in also fitted non-standard weapons alongside their service, the USN 12,500, with some of their capital FlaK 30 and FlaK 38, such as the Danish 20mm ships being fitted with as many as 100 of the guns. Madsen, firing a unique 20 X 120 round, and the
The USN rated the Oerlikon as between eight and ten times more effective in the AA role than the .5", and estimated that it accounted for 32% of
Japanese aircraft destroyed by naval AA fire and the 1.1" USN - were not a great success. Their between Pearl Harbor and 1944, after which the mountings were generally much heavier and more figure dropped to 25%.
complex than most of those for the simple
Many other machine guns and light cannon Oerlikon, but the shells lacked range and destruc-were pressed into British service, particularly in tive power in comparison with the 37mm and
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