The Navy Gun Car mounted a single ex-U.S. Navy 14" (360mm) /50 caliber main gun to an armored railway car. Some thirteen such cars were eventually procured by the Navy's Bureau of Ordnance department for service in France during World War 1 (1914-1918). Design work on the type began in late December 1917 (after America's entry into the war, which occurred back in April). By the end of January in the following year, the design was finalized and construction began in mid-February 1918 under the direction of Baldwin Locomotive Works. Testing followed in April. Five cars were initially completed in an Mk I form. These were broken down into transportable components and shipped for service in France where they were reassembled in July and departed St. Nazaire in August for action. Interestingly, the weapon systems were manned by U.S. Navy personnel.
The gun car made up part of what was a whole column of cars to complete the train. The cars included the requisite locomotive as well as crew cars, equipment support cars and ammunition carriers. The trains were used by the Americans in support of ground actions in pummeling German troop concentrations and fortifications along the various fronts. In addition to their obvious firepower, this sort of weapon also served as a tremendous psychological tool that could not be measured - the large-caliber gun fired a 1,400lb shell upwards of 24 miles away.
The Navy Gun Car Mk I line was improved with the arrival of the Mk II which removed the need to erect a support base for firing the gun at higher angles (this was the case with the Mk I). Eight more cars followed in production though these were completed too late to see combat in the war. They did, however, survive throughout the interwar years to see service in World War 2 as coastal defense weapons. They then were either scrapped or preserved as outdoor showpieces.