20mm Oerlikon Light Antiaircraft Gun


Photograph of 20mm Oerlikon AA gun

National Archives #80-G-71586


Specifications:


Ammunition type Contact fused HE fixed shell, with or without tracer.
HE/incendiary and SAP rounds were also available.
The complete round (projectile plus cartridge) weighed about 0.531 lb (0.241 kg) and was up to 7.18 in (18.2 cm) long.
Projectile weight 0.272 lb
0.123 kg
Velocity 2740 feet/s
835 m/s
Maximum elevation       90 degrees
Range 4800 yards
4390 meters
Altitude 10,000 feet
3050 meters
Rate of fire 480 rounds per minute


The Swiss Oerlikon is usually regarded as a successful design, and it was certainly a vast improvement over heavy machine guns firing solid shot. It won high praise for its performance at the Battle of the Eastern Solomons, where it accounted for at least half of all the Val dive bombers that attacked the American carriers. It was calculated that by September 1944 the Oerlikon had accounted for 32 percent of all identifiable antiaircraft kills by the Pacific Fleet. It was usually shipped in single free-swinging mounts with splinter shields. Fire control was initially based on simple optical sights, but the Mark 14 gyroscopic computing gunsight was developed early in the war. As the war progressed, ships undergoing refit tended to ship additional guns wherever there was enough space on deck to bolt one down, limited only by magazine capacity and top weight. (The single free-swinging mount, gun, and shield weighed about 1700 lbs [770 kg]).

However, the single 20mm proved too light a weapon to fend off the kamikazes. One destroyer commander reported that "when the 20 mm. opens fire, it's time to hit the deck", while another report noted that "20-mm. fire was a signal to the engine room to shut down the blowers to keep the flash of the explosion from the suicide hit being drawn into the machinery spaces" (Friedman 2004). Single mounts were beginning to be replaced by dual or even quadruple mounts by the end of the war. Most of the dual mounts were also free swinging, but a few dual mounts and the quadruple mounts were powered and were directed using a joystick and the Mark 51 director. The latter was a Mark 14 mounted on a "dummy gun".

The sustained rate of fire of most models was much reduced by the need to pause and reload the 60-round magazine. An experimental quad mount using belted ammunition would have had a sustained rate of fire of 150 rounds per minute, but was superseded by by twin 40mm Bofors mounts.

References

Frank (1990)

Friedman (2004)

Campbell (1985)

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