7in Gun on Railway Mount Model 1918

The 7in Gun on Railway Mount Model 1918 mounted a US Navy 7in gun on an army railway car, and was constructed to protect the US coast against U-Boat attack during the First World War.

The original plan had been to develop a drop-platform railway car, similar to the one used on the 4.7in Howitzer on Railway Mount Model 1917, and use it to carry 6in and 8in coastal defence guns. However it was then discovered that these guns would have required a carriage that was too wide for European railways. Twelve cars had already been produced and in 1918 the plan was modified to use Navy 7in guns instead.

The carriage had a dropped centre section and raised ends. The ends were attached to four wheel bogies using hydraulic rams, allowing the entire carriage to be lowered until the centre section was resting on the track. Outriggers were provided to improve stability when firing. It took 45 minutes to install the gun and 25 minutes to prepare it for movement.

The gun was a 7in Mark II Navy gun, with a 45 calibre barrel and an interrupted thread breechblock with a mechanical firing mechanism. It used a hydro-spring recoil system, with the three cylinders mounted below the barrel. The hydraulic recoil cylinder was in the centre, attached to the bottom of the cradle. There were two spring recuperator cylinders mounted on either side of it. The gun could recoil up to 21in.

The normal deck mounting for the gun was too low to allow it to reach its maximum elevation of 15 degrees firing forward or aft when mounted directly onto the car, so an extra cast steel base was added to lift it up. The elevation system involved a rack and pinion system, on the left side of the cradle. It could be traversed through 360 degrees using a worm wheel driven by a wheel on the right side of the cradle.

The gun car was connected to an ammunition car. The projectiles were moved from the ammo car to the ammunition table at the rear of the gun car. This had two side panels that could be lowered to provide a working platform. An ammo working table was provided, and could be moved from one end of the carriage to the other depending on the direction of fire.

After the First World War the railway guns were given to the coastal artillery, and the 7in guns were kept on strength for some time because of their 360 degree traverse.


7in Gun on Railway Mount Model 1918



Barrel Length


Gun length

8.20m (323in)

Weight for transport


Weight in action

77.616kg (171,000lb)


-5 to +15 degrees


360 degrees

Shell Weight

74.80kg (165lb) AP with 1.47kg explosives
69.44kg (153lb) HE with 10.89kg explosives

Muzzle Velocity

822m/ s (2,700 ft/sec)

Maximum Range

15.53km (17,000 yards) at 15 degrees

Rate of Fire

50 rounds/ hour


Books on the First World War | Subject Index: First World War

How to cite this article: Rickard, J (27 December 2018), 7in Gun on Railway Mount Model 1918 , http://www.historyofwar.org/articles/weapons_7in_gun_railway_mount_1918.html

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