The evolution of automatic cannon (that is, of calibres between 20mm and 40mm) between the wars can generally be characterised as a long period of casual development until the late 1930s, followed by a frantic rush to re-equip for the impending conflict.
purposes. There were some exceptions, however. 38, closely related to the FlaK 30 and 38 AA guns
Some of them were intended as anti-tank weapons but carried by aircraft, so they will be dealt with elsewhere. Others were given a dual role, which basically meant developing armour-piercing ammunition so that AA cannon could defend themselves. Only Germany made extensive use of and using the same ammunition. Armour penetration was quoted as 31 mm/100m/60° and 25mm/300m/60° for AP-T ammunition, increased to 49mm and 37mm respectively with PzGr40 Hartkernm an it ion.
automatic cannon as the main armament of light purposes has already been mentioned. However, the only really successful API blowback A A gun was the Oerlikon S. It was used by the British Army in armoured fighting vehicles, although the Russians did fit the 20mm ShVAK aircraft cannon to the T-60 light tank. The Germans used the KwK 30 and a variety of mountings, some with several guns. The
Oerlikon was supplemented in British service during the Second World War by the Polsten, a simplified version developed by Polish engineers. This was only 20% of the cost to manufacture and also lighter, weighing 55kg instead of 67kg, and typically used a thirty-round vertical box magazine instead of the Oerlikon's sixty-round drum. A large number of multiple Oerlikon and Polsten mountings of various types, some fitted to tanks or armoured cars, saw action as a part of the Diver Belt' - the A A
fW^Më tig r
( Courtesy: Ver lag Stocker- Schmid, Dietikon-Zurich )
Quad 20mm Oerlikon S on British 4X4 mounting
(Courtesy: MoD Pattern Room)
Various methods were used to move guns No. 1 (Swiss 20mm
(Courtesy: Verlag Stocker-Schmid, Dietikon-Zurich)
Various methods were used to move guns No.2 (Swiss 20mm Flab. Kan. 38)
(Courtesy: Verlag Stocker-Sclimid, Dietikon-Zurich)
zone established off the south-east coast of England in 1944 to defend against the V-l flying bomb attacks. Somewhat surprisingly, the Polsten were introduced before and during World War Two. Bofors of Sweden produced the m/40 using their own 20 X 145R cartridge, which was totally also appeared as the secondary armament of eclipsed by the commercial success of its 40mm the prototype Centurion tank, but this was not successful.
Several other 20mm AA guns and cartridges design. The Swiss Furrer-designed Flab Kan 38 (Fliegerabwehrkanone 1938) A A gun remained in service until 1947. It was designed around a
Japanese 20 mm Type 98 A A gun
(Courtesy: Mol) Pattern Room )
powerful 20 X 139 cartridge, very similar to the post-war HS 820 round but with a thin-rimmed case which may be brass or steel.
The Danish firm Madsen produced the Model 1935, designed round a large, thick-rimmed 20 X 120 cartridge (also available, although apparently not sold, in a 23 X 106 version). The guns were initially intended for use in aircraft, but saw most service use in the AA role. The Madsen Model 1935 was fitted to a turntable rotating on a cruciform mounting, the whole package weighing 260kg in action (307kg in travelling form). It normally used ten- or fifteen-round magazines, but a sixty-round magazine and belt-fed versions were also available. The equipment was successful, being licence-built in France and Belgium and used by about twenty different nations throughout the world. It is presumably still in use, as 20mm ammunition is still in production.
The Finnish designer Lahti also worked on a number of experimental 20mm cannon between the wars, leading to the L-40 (properly the 20ItK/L-40), a twin AA gun using the 20 X 138B Solothurn cartridge and closely related to the L-39 anti-tank rifle, of which some 200 systems were manufactured up to 1945. The total weight was 652kg, and the rate of fire is variously given as 2 X 700 rpm or 2 X 250 rpm, the latter being rather more likely.
The Japanese produced the largest cartridges of all in this calibre, the 20 X 158 Type 94 and the 20 X 142 Type 98, the latter apparently superseding the earlier weapon, of which few were made. The Type 98, introduced in 1938, used a vertical twenty-round box magazine. It could be fired from its travelling position, on a carriage with large, wooden wheels, but was normally supported on a flat tripod. It weighed 269kg in action. As well as the usual HE shells, the gunners were provided with AP ammunition for its secondary AT role.
One of the most widely used 20mm cannon cartridges was the 20 X 138B round (the long Solothurn', to distinguish it from the 20 X 105B 'short Solothurn") fired by the Wehrmacht s standard light AA guns. The first weapon to introduce this cartridge was the Solothurn S5-100, a direct descendant of the Erhardt introduced in the First World War. This in turn was developed by the parent company of Rheinmetall-Borsig into the FlaK 30, which entered service in 1935 and remained in use throughout the war. The gun was fed by a twenty-round box magazine, which must have provided a lot of work for the reloading crew in an extended engagement.
The FlaK 30 had a rather low rate of fire (280 rpm) and was somewhat prone to jamming so it was supplemented and later supplanted in production
Flakpanzer IV (2cm): 2cm Vierlingsflak 38 on chassis of Pz IV (Imperial War Museum)
by a Mauser-modified version which used the same ammunition and magazines, the FlaK 38. This equalled the Oerlikon Ss rate of fire at around 450 rpm but the cartridge was more powerful with a higher muzzle velocity. The FlaK 38 weighed 406kg in action, compared with 483kg for the FlaK 30.
The FlaK 38 also saw service in a four-barrelled version, the Flakvierling, which weighed 1,520kg and was probably the most formidable short-range AA weapon anywhere in the world until the introduction of the post-war Soviet quad 23mm ZSU-23-4. Both single and quad mountings were fitted to a variety of tracked armoured vehicles, usually redundant tank chassis, to form Flakpanzers. These were desperately needed on the Eastern Front from 1943 onwards to try to protected armoured columns from the marauding 11-2 Shturmovik Italian 20mm Scotti (BuOrd. usn)
The long Solothurn cartridge saw use in a variety of other weapons including two Italian AA guns: the Breda Model 35 and the Scotti. The gas-operated Breda was more common, but had a modest performance with a 200-220 rpm rate of fire, made worse by the feed method which involved a twelve-round strip. The Scotti used a gas-unlocked blowback system similar to the Hispano, but could still achieve only 250 rpm. It was, however, somewhat lighter than the Breda at 227kg in action (including mounting) instead of 307kg, and was available with a twelve-round strip feed, a sixty-round drum magazine or belt feed.
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