The 7-inch Mark 1 was built in a length of 44 calibers, had a
nickel-steel liner, with a
tube, jacket and three
hoops with a locking ring, all made of gun steel, a screw box liner, and
Welin breech block. The Mark 1 was hooped from the breech to from the muzzle. Only one Mark 1 was built, the prototype. The Mark 2 was the production version, it was of the same construction as the Mark 1 except that it was hooped all the way to the muzzle and had one caliber, or seven inches, added to its length. The Mark 2 Mod 1 was constructed with a conical
nickel-steel liner. Two experimental Mark 2 guns, given serial numbers 2 and 3, were built with wider diameter breech ends, with gun No. 2 modified with a conical nickel-steel liner and modified breech, becoming Mark 2 Mod 2. The two
Mississippi-class battleships were transferred to Greece in 1914 with their 7-inch guns. They were sunk in 1941 during World War II. Most of the 7-inch guns were removed from warships before
World War I and some of the Mark II guns were mounted on Mark V tractor mounts that had been designed by the Navy's
Bureau of Ordnance (BuOrd) and built in
Philadelphia, by the
Baldwin Locomotive Works. The mounts were not self-propelled; the tracked mounting was for cross-country mobility, and they would be towed by a
Holt tractor or other vehicle. The
Marines ordered 20 of these guns, with the
Army later ordering 36; before the
Armistice was signed all 20 were delivered to the Marines, while 18 were completed postwar for the Army. The tracked mounting allowed 40° of elevation, for a maximum range of . The Army had requested these guns because of their lack of heavy artillery in France. The 20 guns for the Marines were to go to the new
10th Marine Artillery Regiment that was training at
Quantico, Virginia, in the fall of 1918. The Marines fired the first shot at Lower Station (
Naval Support Facility Dahlgren today) down the
Potomac River, on 16 October 1918. In common with most US-produced heavy artillery in that war, none of the 7-inch guns were shipped to France, or saw action. In 1920, the Army's Ordnance Department described the weapon as: "the heaviest and hardest hitting gun for which a mobile field mount has been requested by our Army". The gun and towed tractor mount are an ancestor of the
self-propelled artillery that has played a major role in most wars since. Also in World War I, twelve 7-inch guns were mounted as
railway artillery for the Army. None were shipped overseas in that war. These appear to have been dismounted and used as coast artillery after the war. However, at least one was transferred to
Brazil, as a railway gun in 1941. Due to the emergency situation at the beginning of
World War II, several of these guns were pressed into service as coastal defense batteries. == Naval service ==