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 Lexington-class battlecruisers, 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 35,000 long tons (36,000 t).
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 Lexington-class aircraft carriers, 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 Iowa-class battleship.
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.
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 Lexington-class battlecruisers, 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 35,000 long tons (36,000 t). 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 Lexington-class aircraft carriers, 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 Iowa-class battleship. 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.
16"/50 caliber Mark 2 gun