| 45 mm anti-aircraft gun (21-K) | |
| Origin: | Soviet Union |
| Type: | Anti-aircraft cannon |
| Is Ranged: | yes |
| Is Artillery: | yes |
| Service: | 1934—? |
| Used By: | Soviet Union |
| Wars: | Second World War, Cold War |
| Design Date: | 1932—34 |
| Production Date: | 1934—1947 |
| Number: | 2799 |
| Variants: | 40-K, 41-K |
| Weight: | 107kg-115kgkg (236lb-254lbkg) |
| Length: | 2.3975m (07.8658feet) |
| Part Length: | 2.0725m (06.7995feet) |
| Cartridge: | 45×386 mm. SR |
| Cartridge Weight: | 1.065- |
| Caliber: | 45mm |
| Action: | single-shot |
| Rate: | 25-30 rpm (practical) |
| Velocity: | 880m/s |
| Range: | 6000m (20,000feet) (maximum ceiling) |
| Max Range: | 9200m (30,200feet) at 45° |
| Breech: | semi-automatic, vertical sliding-block |
| Elevation: | depends on the mount |
| Traverse: | 360° |
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 3.7cm (01.5inches) German weapon designed by Rheinmetall that was sold to the Soviets before Hitler came to power in 1933 that had been enlarged to 45mm 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.
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-automatic breech automatically ejected the cartridge 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 the 40 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]
The 21-K, complete with its pedestal, weighed 507kg (1,118lb). 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 on river monitors. The 40-K was a single gun turret that weighed 2000kg (4,000lb) and the 41-K was a twin-gun turret that weighed 2600kg (5,700lb). 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]
The 21-K used the same ammunition as the 45 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 a time 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 | 1.42kg (03.13lb) | 18g | 760m/s | |
| OT-033 | Fragmentation-tracer | 1.065kg (02.348lb) | 52g | 880m/s | |
| OR-73A | Fragmentation-tracer | 1.41kg (03.11lb) | 37g | 760m/s | |
| F-73 | High-explosive | 1.41kg (03.11lb) | 74g | 760m/s | |
| O-240 | High-explosive | 2.14kg (04.72lb) | 118g | 335m/s |
See main article: 45 mm anti-tank gun M1937 (53-K).