Disappearing gun



A disappearing gun (often called a disappearing carriage) was a type of heavy (mainly coastal) artillery used in the past for which the gun carriage enabled the gun to rotate backwards and down into a pit protected by a wall (the parapet) or a bunker after it was fired. This retraction lowered the gun from view by the enemy while it was being reloaded.

It also made reloading easier, since it lowered the breech to a level just above the loading platform, and shells could be rolled right up to the open breech for loading and ramming. Although it had these advantages, the disappearing carriage was also a complicated mechanism. In the U.S., disappearing carriages were mostly withdrawn from active service by the early 1920s.

The disappearing gun was usually moved down behind the parapet or into its protective housing by the force of its own recoil, which (on many models) lifted a counterweight. Before firing, the crew tripped a catch on the counterweight, causing it to fall into a well at the center of the gun position and move the gun back up "into battery" (firing position).

Some disappearing guns also used compressed air, while a few were built to be raised by steam.

Advantages
The disappearing carriage had several principal advantages:
 * It afforded the gun crew protection from direct fire by raising the gun over the parapet (or wall in front of the gun) only when it was to be fired, otherwise leaving it at a lower level, where it was also able to be loaded easily.
 * With its guns in a retracted position (down behind the parapet), the battery was much harder to spot from the sea, making it a much harder target for attacking ships. Flat trajectory fire tended simply to fly over the battery, without damaging it.
 * Interposing of a moving fulcrum between the gun and its platform lessened the strain on the latter and allowed it to be of lighter construction while limiting recoil travel.
 * Simple, well protected earthen and masonry gun pits were much more economical to construct than the previous practice of constructing the standing heavy walls and fortified casemates of a more traditional gun emplacement.
 * The entire battery could be hidden from view when not in use, unlike a traditional fort, enabling ambuscade fire.

Disadvantages
The disappearing gun had several drawbacks as well:
 * The carriage design restricted maximum elevation to under 20 degrees and thus lacked the necessary range to match newer naval guns entering service during the early part of the 20th century. The additional elevation gained by mounting the same gun on a later non-disappearing carriage increased their range.
 * The time taken for the gun to swing up and down and be reloaded slowed the rate of fire. Surviving records indicate a rate of fire of 1 round per 1 to 2 minutes for an 8-inch (20 cm) gun, significantly slower than less complicated guns.
 * The improvement in the speed of warships demanded an increased rate of firing. The disappearing gun was at a disadvantage compared with a gun that stayed in position as one could not aim or reposition a disappearing gun while it was in the lowered position. The gunner still had to climb atop the weapon via an elevated platform to sight and lay the weapon after it was returned to firing position, or receive fire control information (range and bearing) transmitted from a remote location.
 * Their relative size and complexity also made them expensive compared with non-disappearing mounts.

History
Disappearing guns as a functioning concept were invented in the 1860s by Captain (later Sir) Alexander Moncrieff, who built on his observations in the Crimean War to improve on existing designs for a gun carriage capable of rising over a parapet before being reloaded from behind cover. His key innovation was a counterweight system that raised the gun as well as controlled the recoil. Moncrieff promoted his system as an inexpensive and quickly constructed alternative to a more traditional gun emplacement.

Buffington and Crozier further refined the concept in the late 1880s by incorporating hydro-pneumatic recoil control to assist the counterweight action. The Buffington–Crozier Disappearing Carriage (1893) represented the zenith of disappearing gun carriages, and guns of up to 16-inch size were eventually mounted on such carriages. Disappearing guns were highly popular for a while in the British Empire, the United States and other countries.



However, in the 1890s, a series of Royal Navy/New Zealand Division of the Royal Navy trials carried out in New Zealand (where numerous disappearing guns had been bought and installed during the Russian Scares), revealed the virtual impossibility of a small shore installation being hit by a warship, except by chance. Others dispute that the advantages were so limited, and point to the efficiency of such artillery in for example, the Battle of Port Arthur. In any case, with their protective benefits thus cast into doubt, no further production of the expensive gun carriages was undertaken in New Zealand.

Though effective against ships, the guns turned out to be vulnerable to aerial attack. After World War I batteries of disappearing guns were usually casemated for protection or covered with camouflage for concealment. By 1912, the guns were declared obsolete in the British Army, with only some other countries, particularly the United States, still producing them up to World War I and keeping them active through to the end of World War II.

Gun lift battery
One unique and even more complex type of disappearing gun was Battery Potter at Fort Hancock, Sandy Hook, New Jersey. Built in 1892, the Battery covered the approaches to New York harbor. Instead of using recoil from the gun to lower the weapon, two 12-inch barbette carriages were placed on individual hydraulic elevators that would raise the 110-ton carriage and gun 14 feet to enable it fire over a parapet wall. After firing, the gun was lowered for reloading using hydraulic ramrods and a shell hoist. While the operation of the battery was slow, taking 3 minutes per shot, its design allowed an unlimited field of fire.

Battery Potter required a huge amount of machinery to operate the gun lifts, including boilers, steam pressure pumps and two accumulators. Due to the inability to generate steam quickly, Potter's boilers were run nonstop during its 14-year life, creating a significant operating cost. After the proving of the Buffington Crozier carriage, the United States Army abandoned plans to build several additional gun lift batteries.

Naval artillery
At least once, the concept was also attempted for conversion to a naval use. HMS Temeraire was completed in 1877 with two disappearing gun turrets sinking down into barbette-structures (basically circular metal protective walls over which the gun fired when elevated). This was to combine the ability of the early pivot guns to swivel with the protection of more classical fixed naval guns. However, the design was not successful and apparently never repeated. It is thought that both harsh saltwater environment and the constant swaying and rolling of a ship at sea were to blame for problems with the complex mechanism.