1.1" / 75 Caliber Gun
Quadruple-mount 1.1-inch (28 mm) anti-aircraft cannon aboard the battleship USS Pennsylvania (BB 38) during World War II
Type	Anti-aircraft Naval Gun
Place of origin	United States
Service history
Used by	US Navy
Wars	World War II
Specifications
Weight	10,500 pounds (4,800 kg)
Length	119.6 inches (3.04 m)
Barrel length	82.5 inches (2.10 m) bore (75 calibres)
Shell	HE-Tracer
Caliber	1.1-inch (28 mm)
Recoil	3.25-inch (83 mm)
Elevation	-15 to 110 degrees
Traverse	360 degrees
Rate of fire	150 rpm
Muzzle velocity	2,700 feet per second (820 m/s)
Maximum range	6,300 yards (5,800 m)

The 1.1"/75 caliber gun was an American anti-aircraft weapon of World War II. The name means that it had a bore diameter of 1.1 inches (28 mm) and barrel length of 75 × 1.1 inches = 82.5 inches (2.1 m), using the "caliber" nomenclature common to large artillery pieces.

It was developed when the U.S. Navy Bureau of Ordnance (BuOrd) decided that the .50 caliber machine gun was not adequate for future AA duties:

"In recognition of the growing necessity for antiaircraft fire, the more or less continuous Bureau experimentation with double-purpose guns during the 1920's finally culminated in the early 1930's in the development of the 5"/38 DP gun which fulfilled its mission throughout the war with very little criticism. While the longer range antiaircraft gun field was taken care of, except for insufficient numbers, the situation was far from satisfactory in the short range category. Neither the .50 caliber machine gun, effective enough in plane-to-plane fire at pointblank range, nor the 1.1" which the Bureau developed in quadruple mounts in the 1930's, were competent to meet the menace of the Second World War plane. The 1.1" was too heavy to serve as a "last ditch" free mount and too light to span the gap between the small machine guns and the 5-inch guns, even had all its "bugs" been eliminated. The lack of adequate short range antiaircraft guns together with insufficient quantities of the best guns then available created a situation which by 1940 could hardly be termed anything but critical."^[1]

1.1" mounts firing aboard USS Hornet (CV-8), May 1942.

During the early part of World War II, they were deployed on most U.S. Navy warships of destroyer and larger size.

Due to teething problems that were never rectified, the gun was very unpopular with its crews. It was replaced with the Bofors 40 mm gun whenever possible, but served until the end of the war on some ships.

The guns were sometimes referred to as "Chicago Pianos."

See also[link]

• List of anti-aircraft guns
• List of artillery of the United States

Notes and references[link]

External links[link]

Wikimedia Commons has media related to: 1.1"/75 caliber gun

• navweapons.com 1.1"/75 Gun

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