Three tiers of artillery casemates at the mid-19th century Fort Point, San Francisco. In tanks that do not have a turret for the main gun, the structure that accommodates the gun is also called a casemate. Although the main armament of ships quickly began to be mounted in revolving gun turrets, secondary batteries continued to be mounted in casemates however several disadvantages eventually also led to their replacement by turrets. With the introduction of ironclad warships, the definition was widened to include a protected space for guns in a ship, either within the hull or in the lower part of the superstructure. Although the outward faces of brick or masonry casemates proved vulnerable to advances in artillery performance, the invention of reinforced concrete allowed newer designs to be produced well into the 20th century. Originally, the term referred to a vaulted chamber in a fort, which may have been used for storage, accommodation, or artillery which could fire through an opening or embrasure.

A mid-19th century artillery casemate at Fort Knox, Maine.Ī casemate is a fortified gun emplacement or armored structure from which guns are fired, in a fortification, wardship or armoured fighting vehicle.