During the later half of the 17th Century, military engineers such as Vauban, had devised complex systems for the conducting of sieges that made life very difficult for the defenders. Attempts were therefore made to find a way of concealing an artillery piece and only exposing it when it fired. None of the various proposals appears to have been adopted. The term “Disappearing” gun was not used until February 1886.
By the 1860s the British had moved towards heavily defended gun emplacements with their forts. This entailed a heavy gun in a bombproof casemate with a heavy iron shield to its’ front. Granite, up to fifteen feet thick, held in place the twenty inch thick iron shield. These shielded emplacement came in various forms but proposals were advanced for casemated forts at key locations including nine on the Thames, and at Portsmouth, eight a Plymouth and six in Milford Haven. However, these coastal batteries were costly to build, about £3,850 per emplacement and £1,200 for each gun. Thus Fort Picklecombe in Plymouth, with forty two of these shielded guns on two level cost, cost about one quarter of a million Pounds. Ever mindful of the bottom line, the Ordnance Select Committee were always keen to find cheaper alternatives.
In 1865 Captain Colin Scott Moncrieff submitted his design for a disappearing gun but it was initially rejected as being too complex. Captain Moncrieff took out a Patent the following year and continued to ‘sell’ his invention a Hydropneumatic (HP) gun mount. A review Committee into the Construction, Condition and Cost of the Fortifications reported in 1869. This Committee took a critical look at progress from the 1860 Royal Commission Report. This second Commission was impressed with the Moncrieff Disappearing guns, particularly because it cost only about £1,000 for each pit and £1,350 for each 7-inch gun. This was a considerable saving over the casemated positions with iron shields.