the guns were built by armstrongs (elswick ordnance company) and were originally intended to be mounted as a pair in a twin turret on the japanese battleship "yamashiro" but the order was not completed. hence the breech of the left gun, which became known as "scene shifter", opened to the left which was unusual for a british army gun, while that of the right gun, "boche buster", opened to the right. work on mounting them on railway carriages began in 1916 but was not completed until 1918.