In 1942 the Army switched to the longer barreled 45mm model 1942 AT gun. The Naval version of this gun was designated 21-KM and was 68 calibers long. As an AA gun it had limited effectiveness, due to being only semiautomatic and not having a time fuze, which meant that it needed to make a direct hit in order to destroy a target. Used the same ammunition as the earlier 45 mm/46 21-K.
Used a monobloc barrel. A total of 1,209 guns were made.
| Designation | 45 mm/68 (1.77") 21-KM |
|---|---|
| Ship Class Used On | Many warships 1942 - 1947 |
| Date Of Design | 1942 |
| Date In Service | 1942 |
| Gun Weight | 346.1 lbs. (157 kg) |
| Gun Length oa | 134.33 in (3.412 m) |
| Bore Length | 121.54 (3.087 m) |
| Rifling Length | 104.72 in (2.660 m) |
| Grooves | N/A |
| Lands | NA |
| Twist | N/A |
| Chamber Volume | N/A |
| Rate Of Fire | up to 40 rounds per minute |
| Type | Fixed |
|---|---|
| Weight of Complete Round | FRAG-Tracer (OT-033): 4.41 lbs. (2 kg) HE (O-240): 6.37 lbs. (2.89 kg) FRAG-Tracer (OR-73A): 5.12 lbs. (2.32 kg) |
| Projectile Types and Weights | FRAG-Tracer (OT-033): 2.35 lbs. (1.065 kg) FRAG-Tracer (OR-73A): 3.11 lbs. (1.41 kg) HE (O-240): 4.7 lbs. (2.14 kg) HE (F-73): 3.11 lbs. (1.41 kg) AP (BR-240): 3.13 lbs. (1.42 kg) |
| Bursting Charge | FRAG-Tracer (OT-033): 0.11 lbs. (52 g) FRAG-Tracer (OR-73A): 0.08 lbs. (37 g) HE (O-240): 0.26 lbs. (118 g) HE (F-73): 0.16 lbs. (74 g) AP (BR-240): 0.04 lbs. (18 g) |
| Projectile Length | FRAG-Tracer (OT-033): 4.3 calibers FRAG-Tracer (OR-73A): 4 calibers HE (O-240): 5.6 calibers HE (F-73): 4.7 calibers AP (BR-240): 3.82 calibers |
| Propellant Charge | FRAG-Tracer (OT-033): 0.93 lbs. (0.42 kg) HE (O-240): 0.24 lbs. (0.11 kg) FRAG-Tracer (OR-73A): 0.68 lbs. (0.31 kg) Cartridge for all: 1.32 lbs. (0.6 kg) for all |
| Muzzle Velocity | FRAG-Tracer (OT-033): 3,180 fps (970 mps) FRAG-Tracer (OR-73A): 2,740 fps (835 mps) HE (O-240): 1,125 fps (343 mps) HE (F-73): 2,740 fps (835 mps) AP (BR-240): 2,740 fps (835 mps) |
| Working Pressure | N/A |
| Approximate Barrel Life | 4,000 rounds |
| Ammunition stowage per gun | Usual surface ship loadout: 500 rounds |
| Elevation | Distance |
|---|---|
| Max. Ballistic Range | 11,680 yards (10,680 m) |
| AA Ceiling @ 85 degrees | 21,000 feet (6,400 m) |
| Elevation | Distance |
|---|---|
| Max. Ballistic Range | 5,680 yards (5,194 m) |
| Elevation | Distance |
|---|---|
| Max. Timer Range | 6,340 yards (5,800 m) |
Max effective range was 4,000 m vs both surface and air targets.
Data from:
- "Naval Weapons of World War Two" by John Campbell
- "Sovetskie Boevye Korabli 1941-45: IV Vooruzhnie" (Soviet Warships 1941-45: Volume IV Armament) by A.V. Platonov
- "Entsiklopedia Otechestvennoi Artillerii" (Encyclopedia of Fatherland (Russian) Artillery) by A.V. Shirokorad
Special help from Vladimir Yakubov