6"/47 caliber Mark 16 gun

The '6"/47 caliber Mark 16 gun was a feature of many U.S. light cruisers during World War II.

Two versions of this gun were built, Mod 0 and Mod 1. These guns were primarily mounted in triple turrets to engage surface targets. Late in the war limited number of two-gun dual-purpose ("DP") turrets mounting the same gun were produced capable of engaging air and surface targets.

Today one of the few 6 inch triple gun turrets left in the world is on the museum ship USS Little Rock (CG-4), which is located in the Buffalo and Erie County Naval & Military Park in Buffalo, New York.

6 inch /47 guns
The 6"/47 caliber gun was one of several weapons developed by the United States Navy in the 1930s to fire "super-heavy" armor-piercing projectiles, thus increasing warships' destructive power while complying with the limits on bore diameter set by the London Naval Treaty. Compared with the previous 6"/53 caliber gun, the 6"/47 Mark 16 fired a 130 lb armor-piercing (AP) projectile instead of a 105 lb AP projectile. The arrangement in triple turrets allowed the use of all guns in a broadside; the Omaha-class light cruisers of the 1920s mounted twelve 6"/53 guns but could only use eight in a broadside, due to most of the guns being in single casemated mounts.

Each gun could fire a 130 lb projectile 13 mi. Maximum range at 41 degrees elevation was 14.5 mi. Projectiles varied in weight; an armor-piercing projectile weighed 130 pounds while a high capacity (HC) projectile weighed 105 pounds. Ammunition was semi-fixed (the projectile and the powder casing were separate). The powder case for these guns was housed in a brass canister and weighed 65 lb. The HC projectile could be equipped with mechanical time (MT) or, by late 1942, with variable time (VT) radio proximity fuzes for use against aircraft.

Eight to ten rounds per minute could be fired from each of the 6-inch guns. Each gun weighed 4.31 tons and could be elevated up to 60 degrees. Originally gun ports in the turret faces were cut to allow only 41 degrees elevation, though during World War Two all triple 6 inch/47 gun ports were ordered to be modified to permit the full 60 degrees. The guns could not be loaded at greater than 20 degrees elevation; this reduced the rate of fire when engaging distant surface targets or aircraft. All three guns in each turret were mounted in the same sleeve and thus elevated together, but delay coils permitted "split salvos" to be fired; this cured a shell pattern dispersion problem common to many US cruisers of the 1920s and 1930s. The 105 pound armor piercing shell fired at 2810 feet per second could pierce up to 5 in (127 mm) of hardened armor plate out to 9,200 yards; the 130 pound AP shell introduced just before World War Two fired at 2500 feet per second could penetrate out to 15,700 yards.

Gun barrel lives were 750 to 1050 full charge rounds.

Design
A 6-inch triple turret weighed in at about 70 tons, and each rifle barrel was 23 ft long. The turret rested on a barbette or circular shaft that extended several decks into the ship. Projectiles were stored in a projectile handling room in the lower part of the barbette. Over 900 projectiles could be stored in the projectile handling room. The guns were supplied with projectiles via hoists.

Powder stores were below the projectile handling room and powder hoists fed the guns. Empty powder canisters were ejected from the turret via an ejector port at the back of the turret. When the guns were firing, it was not unusual to see empty brass canisters piling up on the deck behind the turret. The turret itself had 6.5 in of armor plate on its face and could train (turn) to follow its target at ten degrees a second.

Each turret required a crew of 3 officers and 52 enlisted men.

Deployment
As well as ships of the Cleveland-class cruiser, these turrets were also fitted to the Brooklyn-class cruiser, St. Louis, and Fargo-class cruiser class cruisers. The Worcester-class cruisers carried the same type of gun, but in twin dual-purpose (DP) mountings. These were not entirely satisfactory, and a triple DP mounting was proposed to replace them, but was cancelled after World War II.

Weapons of comparable role, performance and era

 * BL 6 inch Mk XXIII naval gun : British equivalent light cruiser gun
 * 15 cm SK C/25 : German equivalent light cruiser gun but firing a lighter shell at higher velocity
 * 15.5 cm/60 3rd Year Type naval gun : Japanese equivalent