A casemate is a fortified gun emplacement or armoured structure from which guns are fired, in a fortification, warship, or armoured fighting vehicle.Webster's New Collegiate Dictionary
When referring to antiquity, the term "casemate wall" means a double city wall with the space between the walls separated into chambers, which could be filled up to better withstand battering rams in case of siege (see ).
In its original early modern meaning, the term referred to a vaulted chamber in a fort, which may have been used for storage, accommodation, or artillery that could fire through an opening or embrasure. 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. 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 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 led to their replacement by turrets as well. In tanks and other armored fighting vehicles lacking a turret for the main gun, the structure accommodating the gun is also called a casemate.
Etymology First recorded in French in the mid-16th century, from the Italian or Spanish , perhaps meaning a slaughterhouse, although it could derive from casa (in the sense of "hut"), and matta (Latin ), "done with reeds and wickers", thus a low-roof hut without windows or other openings set in marshy place. It could also come from casa matta with in the sense of "false". However, it may have been ultimately derived from the Greek (), a gap or aperture.
Antiquity: casemate wall
The term casemate wall is used in the archaeology of Israel and the wider Near East for a double city wall or fortress, with transverse walls separating the space between the two walls into chambers. These chambers could be used for storage or habitation, and could be filled with soil and rocks during a siege to strengthen the outer wall against battering rams.
Casemate walls were thought to have been introduced to the region by the Hittites until the discovery of walls which predated the Hittites' arrival. The earliest uncovered casemate wall, dated to the 16th century BC, is at Ti'inik (Taanach).Emswiler (2020), pp. 7–9. Casemate walls became a common type of fortification in the Southern Levant between the Middle Bronze Age (MB) and Iron Age II. They became more numerous during the Iron Age and peaked in Iron Age II (10th–6th century BC). By the 9th century BC, sturdier solid walls began to replace casemate walls as a response to the battering rams used by the Neo-Assyrian Empire.
Casemate walls could surround an entire settlement; most only protected part of it.Emswiler (2020), p. 4. Three types of casemate walls have been identified: freestanding, integrated (the inner wall was part of the settlement's outer buildings), and filled (the rooms between the walls were filled with soil during construction). The filled type had the advantage of quick but stable construction for particularly high walls.Emswiler (2020), pp. 4–5.
Modern period Land fortification Early modern period
In fortifications designed to resist artillery, a casemate was originally a vaulted chamber usually constructed underneath the rampart. It was intended to be impenetrable and could be used for sheltering troops or stores. With the addition of an embrasure through the scarp face of the rampart, it could be used as a protected gun position.Civilwarfortifications.com In bastion forts, artillery casemates were sometimes built into the flanks of bastions, but in action they quickly filled with smoke making them inoperable and for that reason, had fallen out of favor during the 17th century.
18th and 19th centuries
In the late 18th century, Marc René, marquis de Montalembert (1714–1800) experimented with improved casemates for artillery, with ventilation systems that overcame the problem of smoke dispersal found in earlier works. For coastal fortifications, he advocated multi-tiered batteries of guns in masonry casemates, capable of bringing concentrated fire to bear on passing warships. In 1778, he was commissioned to build a fort on the Île-d'Aix, defending the port of Rochefort, Charente-Maritime. The outbreak of the Anglo-French War forced him to hastily to build his casemated fort from wood but he was able to prove that his well-designed casemates were capable of operating without choking the gunners with smoke.Lloyd 1887, pp. 125–127 The defenses of the new naval base at Cherbourg were later constructed according to his system.Lepage p. 96 After seeing Montalembert's coastal forts, American engineer Jonathan Williams acquired a translation of his book and took it to the United States, where it inspired the Second and Third Systems of coastal fortification; the first fully developed example being Castle Williams in New York Harbor which was started in 1807.
In the early 19th century, French military engineer Baron Haxo designed a free-standing casemate that could be built on the top of the rampart, to protect guns and gunners from the high-angle fire of mortars and howitzers.Civilwarfortifications.com
The advantages of casemated artillery were proved in the Crimean War of 1853–1856, when attempts by the Royal Navy to subdue the casemated Russian forts at Kronstadt were unsuccessful, while a casemated gun tower at Sevastopol, the Malakoff Tower, could only be captured by a surprise French infantry attack while the garrison was being changed.Hogg 1975, pp. 79–82 In the early 1860s, the British, apprehensive about a possible French invasion, fortified the naval dockyards of southern England with curved batteries of large guns in casemates, fitted with laminated iron shields tested to withstand the latest projectiles.Hogg 1975. pp. 87-89
However, in the American Civil War (1861–1865), the exposed masonry of casemate batteries proved vulnerable to modern rifled artillery; Fort Pulaski was breached in a few hours by only ten such guns. In contrast, hastily constructed earthworks proved much more resilient.Hogg 1975, p. 101 This led to casemates for artillery again falling out of favor. In continental Europe, they were often replaced by rotating gun turrets, but elsewhere, large coastal guns were mounted in less expensive concrete gun pits or barbettes, sometimes using disappearing carriages to conceal the gun except at the moment of firing.Hogg 1975, p. 94-95 Casemates for secure barrack accommodation and storage continued to be built; the 1880s French forts of the Séré de Rivières system for example, had a central structure consisting of two stories of casemates, buried under layers of earth, concrete and sand to a depth of , intended to defeat the new high explosive shells.Hogg 1975. p. 104
Towards the end of the century, Imperial Germany had developed a new form of fortification called a feste (German article: Festung#Feste), in which the various elements of each fort were more widely dispersed in the landscape. These works, the first of which was Fort de Mutzig near Strasbourg, had separate artillery blocks, infantry positions, and underground barracks, all built of reinforced concrete and connected by tunnels or entrenchments. Although the main armament of these forts was still mounted in armored turrets, local defense was provided by separate protected positions for field guns; these concrete structures were copied by the French who called them casemates de Bourges (French article: Casemate de Bourges) after the proving ground where they had been tested.
20th century
Following experience gained in World War I, French engineers began designing a new system of fortifications to protect their eastern border, which became known as the Maginot Line. The main element of this line were large underground forts based on the feste principle, whose main armament was in turrets, however the countryside between them was defended by smaller self-sufficient works based on the earlier casemates de bourges, housing either light field guns or anti-tank guns.Kaufmann, Kaufmann & Lang 2017, pp. 10-13 As World War II approached, other European nations adopted similar casemate designs as they offered protection from attacking aircraft. The German Organisation Todt undertook the development of casemates for the large coastal guns of the Atlantic Wall. Built of concrete up to thick, they were thought to be able to withstand any form of attack.Hogg 1975. pp. 141-142 Work by the Western Allies to develop countermeasures that could defeat casemates and other types of bunkers resulted in weapons such as tank-mounted spigot mortars, rocket-assisted projectiles, recoilless rifles, various types of demolition charge and earthquake bombs.Hogg 1975. pp. 143-148
Naval
In warship design, the term "casemate" has been used in several ways, but it generally refers to a protected space for guns within a ship's hull or superstructure.
The first ironclad warship, the (1858), was a wooden steamship whose hull was covered with armored plating, tested to withstand the largest smoothbore guns available at the time. The response by the British Royal Navy to this perceived threat was to build an iron-hulled frigate, . However, it was realised that to armor all of the hull to fully withstand the latest rifled artillery would make it unfeasibly heavy, so it was decided to create an armored box or casemate around the main gun deck, leaving the bow and stern unarmored.
The American Civil War saw the use of casemate ironclads: armored steamboats with a very low freeboard and their guns on the main deck ('Casemate deck') protected by a sloped armoured casemate, which sat atop the hull. Although both sides of the war used casemate ironclads, the ship is mostly associated with the Confederate States Navy, as the United States Navy employed turreted monitors, which the Confederacy failed to produce. The most famous naval engagement of the war was the Battle of Hampton Roads between the turreted ironclad and the casemate ironclad (built from the scuttled remains of ).Civilwarhome.com
"Casemate ship" was an alternative term for "central battery ship" (UK) or "center battery ship" (US).Hovgaard, William, Modern History of Warships, pp. 14–15. The casemate (or central battery) was an armored box that extended the full width of the ship, protecting many guns. The armored sides of the box were the ship's sides, or hull. There were armored bulkheads at the front and rear of the casemate, and a thick deck protecting the top. The lower edge of the casemate sat on top of the ship's belt armour. Some ships, such as (laid down 1873), had a two-story casemate.Hovgaard, William, Modern History of Warships, p. 18.
A "casemate" was an armored room in the side of a warship, from which a gun would fire. A typical casemate held a 6-inch gun, and had a front plate (forming part of the side of the ship), with thinner armor plates on the sides and rear, with a protected top and floor,Hovgaard, William, Modern History of Warships, pp. 78–79. and weighed about 20 tons (not including the gun and mounting).Brown, David K., Warrior to Dreadnought, p. 129. Casemates were similar in size to turrets; ships carrying them had them in pairs, one on each side of the ship.