45 mm anti-aircraft gun (21-K)

45 mm anti-aircraft gun (21-K)
A 21-K on board the Krasny Kavkaz
Type	Anti-aircraft cannon
Place of origin	Soviet Union
Service history
In service	1934—?
Used by	Soviet Union
Wars	Second World War, Cold War
Production history
Designed	1932—34
Produced	1934—1947
No. built	2799
Variants	40-K, 41-K
Specifications
Mass	107–115 kilograms (236–254 lb)
Length	2.3975 metres (7.866 ft)
Barrel length	2.0725 metres (6.800 ft)
Shell	45×386 mm. SR
Shell weight	1.065–2.14 kg (2.35–4.72 lb)
Caliber	45 millimetres (1.8 in)
Action	single-shot
Breech	semi-automatic, vertical sliding-block
Elevation	depends on the mount
Traverse	360°
Rate of fire	25-30 rpm (practical)
Muzzle velocity	880 metres per second (2,900 ft/s)
Effective firing range	6,000 m (20,000 ft) (maximum ceiling)
Maximum firing range	9,200 metres (10,100 yd) at 45°

The 45 mm anti-aircraft gun (21-K) was a Soviet design adapted from the 45 mm anti-tank gun M1932 (19-K). This was a copy of a 3.7 cm (1.5 in) German weapon designed by Rheinmetall that was sold to the Soviets before Hitler came to power in 1933 that had been enlarged to 45 mm (1.8 in) to reuse a large stock of old 47mm ammunition. It was used by the Soviet Navy to equip almost all of their ships from 1934 as its primary light anti-aircraft gun until replaced by the fully automatic 37 mm 70-K gun from 1942 to 1943. It was used in World War II and during the Cold War as the Soviets exported their World War II-era ships to their friends and allies. However it was not very effective as its slow rate of fire and lack of a time fuze required a direct hit to damage targets.