16"/50 caliber Mark 7 gun

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A cutaway of a turret mounting 16in guns

Yard workers hoist one of nine 16"/50 Mark VII gun barrels aboard the USS Iowa during her construction in 1942

The Iowa class battleship USS Iowa (1980s configuration, note missile launchers amidships) fires a full broadside of her 16"/50 Mark 7 guns. Note the shock waves reflected in the ocean's surface on the firing side of the ship; these are due to muzzle blast and not from movement of the ship.

The 16"/50 caliber Mark 7 - United States Naval Gun was originally intended to fire the relatively light 2,240 pound (1,016 kg) Mark 5 armor piercing shell, the shell handling system for these guns was redesigned to use the "super-heavy" 2,700 pound (1225 kg) APC (Armor Piercing, Capped) Mark 8 before any of the Iowa-class battleships were laid down. This heavier projectile made these guns nearly the equal in terms of penetration power to the 460 mm (18.1 in) guns of the Japanese Yamato class battleships yet weighed less than three-quarters as much. Due to a lack of communication in the design phase, the Bureau of Ordnance assumed that the Iowa class would use the 16"/50 Mark 2 guns constructed for the 1920 South Dakota-class battleships. However, the Bureau of Construction and Repair assumed that the ships would carry a new, lighter, more compact 16"/50 and designed the ships with barbettes too small to accommodate a 16"/50 Mark 2 triple turret. The new 16"/50 Mark 7 was designed to resolve this conflict.

The weapon is constructed of liner, tube, jacket, three hoops, two locking rings, tube and liner locking ring, yoke ring and screw box liner. Some components were autofretted. Typical of United States naval weapons built in the 1940s, the bore was chromium plated for longer barrel life. Uses a Welin breech block that opens downwards and is hydraulically operated. The screw box liner and breech plug are segmented with stepped screw threads arranged in fifteen sectors of 24 degrees each.

Gun Characteristics

Designation	16 in/50 caliber (406 mm × 20.3 m) Mark 7
Ship Class Used On	Iowa (BB-61) and Montana (BB-67) classes
Date Of Design	1939
Date In Service	1943
Gun Weight	267,904 lb (121,519 kg) (including breech) 239,156 lb (108,479 kg) (without breech)
Gun Length oa	816 in (20.73 m) (breech face to muzzle)
Bore Length	800 in (20.32 m)
Rifling Length	682.9 in (17.34 m)
Grooves	(96) 0.150 in deep (3.81 mm)
Lands	N/A
Twist	Uniform RH 1 in 25
Chamber Volume	27,000 in³ (0.44 m³)
Rate Of Fire	2 rounds per minute
Note: The primer cartridge can be either electric or percussion fired.
Range	41,622 yards or 23.64miles w/ nominal 660lbs. powder charge
Muzzle Velocity	2690fps