----------------+---------+----------+--------------------------- Number of guns. | Size. | Length. | Source whence obtained. ----------------+---------+----------+--------------------------- | Inches. |Calibers. | 12 | 7 | 45 | Navy. 96 | 8 | 35 | Seacoast defenses. 129 | 10 | 34 | Do. 49 | 12 | 35 | Do. 6 | 12 | 50 | In manufacture for Chile. 150 (mortars) | 12 | 10 | Seacoast defenses. 21 | 14 | 50 | Navy. ----------------+---------+----------+--------------------------- In addition to these there was the 16-inch howitzer, 20 calibers in length, which had been built by the Ordnance Department before 1917. The expression 14-inch gun, 50 calibers, means that the gun has a barrel diameter of 14 inches and that the gun body is fifty times the caliber of 14 inches, or 700 inches (58 feet 4 inches) long. The Ordnance Department conceived that the only way to make these guns available for use abroad would be to mount them on railway cars. These guns were not vital in the defense of our coast under the conditions of the war with Germany, but it was evident that they would make a valuable type of long-range artillery when placed on satisfactory railway mounts. Mounting heavy artillery on railway cars, however, was not an idea born of the recent war. The idea was probably originally American. The Union forces at the siege of Richmond in 1863 mounted a 13-inch cast-iron mortar on a reinforced flat car, this being the first authenticated record of the use of heavy railway artillery. In 1913 the commanding officer of the defenses of the Potomac, which comprise Forts Washington and Hunt, was called upon to report on the condition of these defenses. In reply, he advised that no further expenditure be made on any one of the fixed defenses, but recommended that a "strategic railroad" be built along the backbone of the peninsula from Point Lookout to Washington, with spurs leading to predetermined positions both on Chesapeake Bay and the Potomac River, so placed as to command approaches to Washington and Baltimore. Further, he recommended that 4 major-caliber guns, 16 medium-caliber guns, and 24 mine-defense guns be mounted on railroad platforms, with ammunition, range finding, and repair cars making up complete units, so that this armament could be quickly transported at any time to the place where most needed. He suggested that this scheme be made applicable to any portion of the coast line of the United States. His argument was based upon the fact that guns in fixed positions, of whatever caliber, violate the cardinal military principle of mobility.