 The disappearing gun was usually moved down behind the parapet or into its protective housing by the force of its own recoil, but some also used compressed air while a few were built to be raised by steam.Captain (later Colonel Sir) Alexander Moncrieff improved on existing designs for a gun carriage capable of rising over a parapet before being reloaded from behind cover.His design, based on his observations in the Crimean War was the first widely adopted, used in many forts of the British Empire.