|Used by||Royal Air Force|
|Wars||Second World War|
|Variants||Mk 1, Mk 2|
|Weight||320 lb (134 kg)|
|Length||9 ft 9 inches (2.97 m)|
|Barrel length||1.70 m|
|Cartridge weight||4 lb|
|Rate of fire||100 rounds/min|
|Muzzle velocity||1,870 ft/s with 3lb shot|
|Feed system|| 12-round drum|
later 15 rounds
The Vickers Class "S" 40 mm (1.57 in) gun was developed in the late 1930s as an aircraft weapon. The ammunition was based on the 40x158R cartridge case of the naval 2 pdr Anti-aircraft gun (the "Pom-pom"). The weapon was a long-recoil design derived from the 37 mm 1½pdr "COW gun" from Coventry Ordnance Works.The gun was originally intended as a bomber defensive weapon and was tested as such in a turret fitted to a modified Vickers Wellington II. This was not adopted for service, but when the need to attack tanks from the air was identified, the "S" gun was chosen and special armour-piercing ammunition developed.
Two underwing guns were fitted to Hawker Hurricane IID fighters which were issued to No. 6 Squadron RAF. They served in North Africa from mid-1942 where they achieved considerable success; claims included 148 tanks hit, of which 47 were destroyed, plus nearly 200 other vehicles. However, they suffered heavy losses, mainly to ground fire (the Hurricanes were poorly protected) and also lacked effectiveness against the Tiger tank. In 1944, the aircraft served in the Far East, mainly firing HE ammunition against road and river transports.
Tests in the Far East showed a high level of accuracy, with an average of 25% of shots fired at tanks striking the target. Attacks with HE were twice as accurate as with AP, possibly because the ballistics were a closer match to the .303 in (7.7 mm) Browning machine guns used for sighting (the HE shell was lighter and was fired at a higher velocity). By comparison, the practice strike rate of the 60 pdr RPs (rocket projectiles) fired by fighter-bombers was only 5% against tank-sized targets.
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- Anthony G Williams, 37MM AND 40MM GUNS IN BRITISH SERVICE
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