Disappearing gun

The overwhelming majority of carriage designs enabled the gun to rotate backwards and down behind a parapet, or into a pit protected by a wall, after it was fired; a small number were simply barbette mounts on a retractable platform.

A late exception was the use in mountain fortifications in Switzerland, where six 120 mm guns on rail-mounted Saint Chamond disappearing carriages remained at Fort de Dailly until replaced in 1940.

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[4] while a few were built to be raised by steam.

[5] Captain (later Colonel Sir) Alexander Moncrieff[6] improved on existing designs for a gun carriage capable of rising over a parapet before being reloaded from behind cover.

[8] The usefulness of such a system had been noted earlier, and experimental designs with raisable platforms or eccentric wheels, with built-in counterweights, were built or proposed.

This used a counterweight to allow a 15-inch (381 mm) Rodman gun to be moved up and down a swiveling ramp, so the weapon could be reloaded, elevated, and traversed behind cover.

It was not adopted; an 1881 letter to the Chief of Engineers by Lt. Col. Quincy A. Gillmore stated that it "still leaves a great deal of heavy work to the slow and uncertain process of manual labor".

[9] Buffington and Crozier further refined the concept in the late 1880s by allowing the counterweight fulcrum to slide, giving the gun a more elliptical recoil path.

[3][11] The only major campaign in which US disappearing guns played a part was the Japanese invasion of the Philippines, which began shortly after the attack on Pearl Harbor on 7 December 1941 and ended with the surrender of US forces on 6 May 1942.

[21] Battery Potter required much machinery to operate the gun lifts, including boilers, steam-powered hydraulic pumps, and two accumulators.

Due to the inability to generate steam quickly, Battery Potter's boilers were run nonstop during its 14-year life, at significant cost.

It has been suggested that both the harsh saltwater environment and the constant swaying and rolling of a ship at sea caused problems for the complex mechanism.

It was a resounding commercial success; there were 21 direct copies,[23] and another six near-sisters,[24] plus six near-copies (see List of gunboat and gunvessel classes of the Royal Navy).

These mounts were intended for use in prepared trench-type positions that would shelter them from view when retracted; in the Swiss forts they were stored in covered bunkers until repositioned to fire.

[14] Retractable turrets were also conceptually similar, but almost never depended on recoil actuation, and, like the balanced pillar systems, often remained visible when actually in operation.

Unlike balanced pillar designs, the pieces could generally be pointed and trained from cover, allowing complete surprise for the first shot.