16"/50 caliber Mark 2 gun

The 16"/50 caliber Mark 2 – United States Naval Gun was a gun originally designed and built as the main armament for the South Dakota–class battleships and s, neither of which was completed. At the time, they were among the heaviest guns built for use as naval artillery, though none of the ships designed for them were ever completed.

History
The first example of a US Navy 16-inch gun was approved for construction in 1895, and completed in 1902. The second design, the Mark 2, was developed intended as armament for the planned South Dakota–class battleships, and also selected for the modified design of the s, replacing the 14"/50 caliber gun that was originally used for the design.

With the United States entering into the Washington Naval Treaty, the terms limited the United States to a maximum displacement of 35000 LT. As both the South Dakota–class battleships and Lexington-class battlecruisers exceeded this limit, the Navy was required to cancel their construction, doing so in 1922. While two of the Lexington class were re-ordered as s, none of them were completed with the barbettes necessary to mount these guns. The existing guns were transferred to the Army and installed in coastal defense batteries in place of the Army's more massive and much more expensive M1919 16 inch Coast Gun.

In 1938, with the signing of the Second London Naval Treaty, the tonnage limits for battleships was relaxed, to 45,000 tons. After this, the U.S. Navy began design of a ship that would fit these higher tonnage limits, eventually resulting in the. The larger size would allow for guns with a 16-inch caliber and a 50-caliber length, larger than the 16"/45 guns used on preceding classes of battleship. While the Iowa-class battleships were under construction, the Bureau of Ordnance assumed that the guns to be used would be the existing Mark 2 design, and through miscommunication, the Bureau of Construction and Repair assumed the ships would use a lighter design. As a result, the Mark 2 guns were not used for these, and the 16"/50 caliber Mark 7 gun was designed instead. The Mark 2 guns were never placed on any ship.

Description
These built-up guns were 67 ft long—50 times their 16 in bore, or 50 calibers from breechface to muzzle. With a full powder charge of 648 lb, the guns were capable of firing a 2240 lb armor-piercing shell with a muzzle velocity of 2650 ft/s firing out to an effective range of 44680 yards.