16-inch/50-caliber Mark 7 gun
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The 16"/50 caliber Mark 7 – United States Naval Gun is the main armament of the Iowa-class battleships and was the planned main armament of the cancelled Montana-class battleship. Wikipedia
Length: 816 in (68.0 ft; 20.7 m)
Shell: AP Mark 8: 2,700 lb (1,225 kg); HC Mark 13: 1,900 lb (862 kg); Nuclear Mark 23 (W23): 1,900 lb (862 kg)
Caliber: 16 in (406 mm)
In service: 1943–1992
Mass: 267,904 lb (121,519 kg; 121.519 t) (including breech)
Maximum firing range: 29 mi (47 km), (23.64 mi (38.04 km) accurately)
Used by: U.S. Navy