| 45 mm anti-aircraft gun (21-K) | |
|---|---|
 A 21-K on board theKrasny 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, verticalsliding-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° |
The45 mm anti-aircraft gun (21-K) was a Soviet design adapted from the45 mm anti-tank gun M1932 (19-K). This was a copy of a 3.7 cm (1.5 in) German weapon designed byRheinmetall that was sold to the Soviets beforeHitler 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 theSoviet Navy to equip almost all of their ships from 1934 as its primary lightanti-aircraft gun until replaced by the fully automatic 37 mm70-K gun from 1942 to 1943. It was used inWorld War II and during theCold War as the Soviets exported their World War II-era ships to their friends and allies. However it was not very effective as its slowrate of fire and lack of a time fuze required a direct hit to damage targets.
The 46-caliber21-K was a minimal adaptation of the 53-K anti-tank gun that was created by taking the latter's barrel and mounting it on a simple pedestal mount. Its semi-automaticbreech automatically ejected thecartridge case and locked open, ready for the next round. This was less than ideal for an anti-aircraft weapon that relied on its rate of fire to inflict damage on aircraft because every round had to be hand-loaded.[1] Fully automatic weapons of roughly this caliber like the40 mm Bofors typically used 4-5 round clips of ammunition to produce rates of fire four times as high.
Early production guns had a built-up barrel, but later ones used a monobloc. There were problems with the breech mechanism early in the production run and a number of the first year's production run lacked the semi-automatic breech entirely.[2]
The21-K, complete with its pedestal, weighed 507 kg (1,118 lb). It was manually operated and could elevate between -10° and +85° at a rate between 10 and 20 degrees per second. It could traverse a full 360° at a rate between 10 and 18 degrees per second, although this was practically limited by its actual location on ship. In the mid-1930s special powered turrets were developed for use onriver monitors. The40-K was a singlegun turret that weighed 2,000 kg (4,400 lb) and the41-K was a twin-gun turret that weighed 2,600 kg (5,700 lb). Both turrets could elevate between -5° and +85° at a rate of 8 degrees per second and could traverse a full 360° at a rate between 4.8 and 9.8 degrees per second.[2]
The21-K used the same ammunition as the45 mm anti-tank gun M1937 (53-K). The biggest problem in its role as an anti-aircraft gun was that it wasn't provided with atime fuze that would detonate the shell at a specified distance from the gun. This meant that only a direct hit would damage its target.[2]
| Shell name | Type | Weight | Filling Weight | Muzzle velocity |
|---|---|---|---|---|
| BR-240 | armor-piercing | 1.42 kg (3.1 lb) | 18 g (0.63 oz) | 760 m/s (2,500 ft/s) |
| OT-033 | Fragmentation-tracer | 1.065 kg (2.35 lb) | 52 g (1.8 oz) | 880 m/s (2,900 ft/s) |
| OR-73A | Fragmentation-tracer | 1.41 kg (3.1 lb) | 37 g (1.3 oz) | 760 m/s (2,500 ft/s) |
| F-73 | High-explosive | 1.41 kg (3.1 lb) | 74 g (2.6 oz) | 760 m/s (2,500 ft/s) |
| O-240 | High-explosive | 2.14 kg (4.7 lb) | 118 g (4.2 oz) | 335 m/s (1,100 ft/s) |
Media related to45mm/46 21-K gun at Wikimedia Commons