The principle of the disappearing carriage was developed by Capt Moncrieff in the early 1860's with the idea of concealing a gun in a pit in the ground instead of inside expensive iron and granite fortresses. After a considerable struggle with the Board of Ordnance his idea was adopted and came into service circa 1870. He was awarded 10,000 for his invention and by 1884 he had been promoted to the rank of Colonel. His idea was effective until the coming of aircraft.