U.S. 1.1"/75 Mark 1 Antiaircraft Gun

Photograph of 1.1" quad AA gun mount

U.S. Navy. Via Wikimedia Commons


Ammunition Type
Fixed contact fused HE shells
Weight of projectile 0.917 lbs
0.416 kg
Velocity 2700 feet per second
823 meters per second
Maximum elevation       90 degrees
Range 7400 yards
6770 meters
Altitude 19,000 feet
5790 meters
Rate of fire 150 rounds per minute

This was the standard light antiaircraft armament on U.S. warships at the start of the war. It was always shipped in quadruple mountings. Although considerable effort and expense was spent on its development, it turned out to be a poor weapon, with numerous design defects and too low a rate of traverse for a gun firing so light a projectile.  There was a particular tendency for the gun to break down due to a weak recoil and ejection mechanism. The 1.1" was therefore replaced by the much superior Oerlikon and Bofors as rapidly as production permitted.  Ammunition came in eight-round clips, which seriously limited the effective rate of fire, and there was a dangerous tendency for the ammunition to detonate prematurely in the hot gun barrels during extended firing

Early installations did not even come with a director, which was judged unnecessary for directing fire against dive bombers heading directly for a ship. The Navy eventually realized that this was a mistake, and the Mark 44 gunsight director began reaching the fleet by summer of 1941.

Photo Gallery

1.1" guns on cruiser Astoria fire at a seaplane

U.S. Navy


Campbell (1985)

Friedman (2013)
Wildenberg (1996)

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