45 mm anti-aircraft gun

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.

• Name — 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 — 107 - • Length — 2.3975 m • Part Length — 2.0725 m • Cartridge — 45×310 mm. R • Cartridge Weight — 1.065 - • Caliber — 45 mm • Action — single-shot • Rate — 25-30 rpm (practical) • Velocity — 880 m/s • Range — 6000 m (maximum ceiling) • Max Range — 9200 m at 45° • Breech — semi-automatic, vertical sliding-block • Elevation — depends on the mount • Traverse — 360°

The 46-caliber 21-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. 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.

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. • Shell name — Type — Weight — Filling Weight — Muzzle velocity • BR-240 — armor-piercing — 1.42 kg — 18 g — 760 m/s • OT-033 — Fragmentation-tracer — 1.065 kg — 52 g — 880 m/s • OR-73A — Fragmentation-tracer — 1.41 kg — 37 g — 760 m/s • F-73 — High-explosive — 1.41 kg — 74 g — 760 m/s • O-240 — High-explosive — 2.14 kg — 118 g — 335 m/s