battleship, including 12 16"/50 Mark 2 guns. The first example of a US 16-inch gun was an
Army weapon,
the M1895, approved for construction in 1895 and completed in 1902; only one was built. The first US Navy 16-inch gun was the
16-inch/45 caliber Mark 1 gun, which armed the
Colorado-class battleships launched 1920–21. The second Navy design, the Mark 2, was intended as armament for the planned
South Dakota-class battleships, and also selected for the modified design of the s, replacing the
14-inch/50 caliber gun that was originally used for the design. The Mark 3 was a slightly modified version of the Mark 2. With the United States entering into the
Washington Naval Treaty, the terms limited the United States to a maximum displacement of . 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. Construction of the 16-inch Mark 2 and Mark 3 guns was also cancelled with 70 completed, plus the prototype, Gun No. 42. Twenty of the existing guns were transferred to the Army in 1922 to supplement the Army's more massive and much more expensive
16-inch gun M1919, of which only seven were ever deployed. The remaining Mk2/Mk3 guns were retained for use on future warships. With funding lacking until 1940, five batteries of two Mk2/Mk3 guns each were built 1924–40 in the
harbor defenses of
Pearl Harbor, the
Panama Canal Zone (Pacific side), and
San Francisco. They were designated 16-inch Navy guns MkIIMI and MkIIIMI in Army service. A version of the M1919
barbette mount used for the M1919 guns was used for these batteries, except at
Fort Funston in San Francisco, where Battery Davis was the prototype for the M2 mount and
casemating. Based on the Coast Artillery's experience operating heavy weapons in World War I, especially the French-made
400 mm (15.75 inch) Modèle 1916 railway howitzer, all barbette carriages for 16-inch guns were designed with an elevation of 65 degrees to allow
plunging fire as enemy ships approached. In 1938, with the signing of the
Second London Naval Treaty, the tonnage limit for battleships was relaxed to 45,000 tons. After this, the U.S. Navy began design of a ship that would fit this higher tonnage limit, 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-inch/45 caliber Mark 6 guns used on the
North Carolina- and
South Dakota-class battleships. 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 and 3 weapons, and through miscommunication, the
Bureau of Construction and Repair assumed the ships would use a lighter design. As a result, the Mark 2 and 3 guns were not used for these, and the
16-inch/50 caliber Mark 7 gun was designed instead. The Mark 2 and 3 guns were never placed on any ship. == Design ==