12in Gun 50 Calibre Gun on Railway Mount (sliding)

The 12in 50 calibre gun on railway mount combined American guns originally built for export with French sliding railway gun mounts. Three had been completed by the end of the war in 1918, but none reached France and the type was soon scrapped after the war.

The guns were 12in 50 calibre Model 1918 Bethlehem guns, with fixed trunnions and a counterweight on the breech end to allow the trunnions to be placed close to the breech, to allow the gun to be fired at high elevation without constructing a firing pit. They used a Welin or step thread breech.

The 12in guns were given no recoil mechanism, and were connected directly to the side girders of the carriage. The sliding recoil mechanism needed a specially prepared section of track. This had extra long ties, which were linked by eight lines of 12in 55lb steel ‘I’ beams. Ten sleepers were mounted below the gun carriage, and could be lowered onto the ‘I’ beams so that the weight of the gun carriage was carried on them. The gun carriage would be moved into place by a locomotive, and then its position fine tuned using its aiming mechanism (see below). When fired the carriage would move back a fairly short distance, the sleepers would be raised, and it would be moved back into place.

Elevation was controlled using a segmental circular rack attached to the side of the counterweight, and controlled by a pinion connected to two hand wheels via gears. One turn of the hand wheel raised or lowered the gun by 0.625 degrees. The gun could be raised from the loading position of -4 degrees up to 40 degrees, and could be fired at 15 degrees or above.

In order to aim the gun it had to be moved along a special section of curving railway track. This could be done manually from the carriage, using a translating mechanism built onto each of the eight wheeled railway trucks that carried the gun. This connected one axle to a hand wheel via a series of gears and chains. Each hand wheel could be operated by four men, and 100 turns of the wheel turned the truck wheel once. In tests eight men, four at each end, could move the entire piece at a rate of 3ft per minute. This system could be used to move the gun in either direction. An alternative, using a 50hp petrol engine, could be used to move it forwards only. One carriage was given electric motors powered by a 25kw generator.


12in Gun 50 Calibre Gun on Railway Mount



Barrel Length


Gun Length

15.44m (608in)

Life of barrel at full charge


Weight in action

249,645kg (550,000lb)


15 to 40 degrees



Shell Weight

317.73kg (700lb) HE, 42.66kg explosives

Muzzle Velocity

975m/ s (3,200 ft/s)

Maximum Range

41.14km (45,000 yards)

Rate of Fire

20 rounds/ hour

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

How to cite this article: Rickard, J (25 February 2019), 12in Gun 50 Calibre Gun on Railway Mount (sliding) , http://www.historyofwar.org/articles/weapons_12in_50_calibre_railway.html

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