The 8-inch Navy gun Mk.VI M3A2 on railway mount M1A1 was a World War II improved replacement for the World War I-era 8-inch (203 mm) M1888 gun and was used by the US Army's Coast Artillery Corps in US harbor defenses.

It was developed from an experimental 12-inch (305 mm) railway howitzer carriage of World War I.

[3] The all-around rotating mount and outriggers were designed to allow the gun to track a moving target for coast defense.

These guns had a very short life in Army use, entering service in February 1941 and being cut up for scrap immediately after the war.

The guns were the Navy's 8-inch (203 mm)/45 caliber Mark VI, and were originally secondary armament on Virginia- and Connecticut-class battleships launched 1904-06 and scrapped in the 1920s.