8"/55 caliber gun

The 8"/55 caliber gun (spoken "eight-inch-fifty-five-caliber") formed the main battery of United States Navy heavy cruisers and two early aircraft carriers. United States naval gun terminology indicates the gun fired a projectile 8 inches (203 mm) in diameter, and the barrel was 55 calibers long (barrel length is 8 inch × 55 = 440 inches or 11 meters).

Mark 9
These built-up guns weighed about 30 tons including a liner, tube, jacket, and five hoops. A down-swing Welin breech block was closed by compressed air from the gas ejector system. Loading with two silk bags each containing 45-pounds (20 kg) of smokeless powder gave a 260-pound (120 kg) projectile a velocity of 2800 feet per second (850 m/s). Range was 31860 yd at the maximum elevation of 41 degrees.

Mark 12
These simplified built-up guns eliminated hoops to reduce weight to 17 tons. The breech mechanism was similar and loading two silk bags each containing 43-pounds (20 kg) of smokeless powder gave a 335-pound (152 kg) projectile a velocity of 2500 feet per second (760 m/s). Each gun could fire about four rounds per minute. Maximum range was 30050 yd at the maximum elevation of 41 degrees.

Mark 14
These guns were similar to Mark 9, with the same shell weight and maximum range, with a smaller chamber and rifling twist increased from 1 in 35 to 1 in 25 in a chromium-plated bore.

Mark 15
These guns were similar to Mark 12, with the same shell weight and maximum range, with the smaller chamber of the Mark 14 gun. Useful life expectancy was 715 effective full charges (EFC) per liner.

Mark 16
These self-loading guns with lined monobloc construction and vertical sliding breech blocks weighed about 20 tons. Semi-fixed ammunition (projectile and powder case handled separately) with 78 pounds (35 kg) of smokeless powder gave a 335-pound (152 kg) projectile a velocity of 2500 feet per second (760 m/s). Each gun could fire about ten rounds per minute. Useful life expectancy was 780 EFC per liner. Range was 17 miles (27 kilometers) at the maximum elevation of 41 degrees. This gun was modified for the experimental Major Caliber Lightweight Gun.

Weapons of comparable role, performance and era

 * 203mm/50 Modèle 1924 gun French equivalent
 * 20.3 cm SK C/34 Naval gun German equivalent
 * 203 mm /53 Italian naval gun Italian equivalent
 * 20 cm/50 3rd Year Type naval gun Japanese equivalent
 * BL 8 inch Mk VIII naval gun UK equivalent
 * 8"/55 caliber Mark 71 gun