Casemate A casemate , sometimes rendered casement , is a fortified gun emplacement or armored structure from which guns are fired . Originally , the term referred to a vaulted chamber in a fortress . In the context of armoured fighting vehicle s , this usually refers to those with a main gun that lack a turret . Origin of the term . The word comes from the Italian " casamatta " , the etymology of which is uncertain . Some theorize that " casamatta " comes from " casa " , Italian for " house " , and " matto " , Italian for " mad " , but in this case meaning " fake " ; " casamatta " seems to have been a common nickname given to a medieval siege machine called gatta , which had the appearance of a house . Others ( Devic ) think that it comes from the Arabic word " kasaba " , transliterated to kasbah , the word that originated the Spanish word for fortress : " alcazaba " . Menagio theorised it came from the Greek word for pit , " khasma " , the plural of which is " khasmata " . Hensleigh Wedgwood thought that it came from the Spanish " casa " and " matar " , making a casemate " a house in which killing happens " . Others take " matto " in its archaic Italian meaning of " dark " , equivalent to the English " matt " , as in " opaque " , making a " casamatta " a " dark house " . " Casematte " were also used as military prisons , making use of their lack of light to add to the punishment . This explanation seems to be the most agreed upon . Usage . Land fortification . 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 . 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 . Casemates built in concrete were used in the Second World War to protect coastal artillery from air attack . Naval . In warship design the term casemate has been used in a number of ways . Casemate ironclads ( American Civil War ) . 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 on top of the hull . Although both sides of the civil war used casemate ironclads , the ship is mostly associated with the southern confederacy , as the north also employed turreted monitor s , which the south was unable to produce . The most famous naval battle of the war was the duel at Hampton Roads between the Union turretted ironclad USS " Monitor " and the Confederate casemate ironclad CSS " Virginia " ( built from the scuttled remains of the " Merrimack " ) . Casemate ships ( 1864 - 1880 ) . " Casemate ship " was an alternative term for " central battery ship " ( UK ) or " center battery ship " ( US ) . The casemate ( or central battery ) was an armoured box the full width of the ship protecting many guns . The armoured sides of the box , were the sides of hull of the ship . There was an armoured bulkhead 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 ship ' s belt armour . Some ships , such as the " Alexandra ( laid down 1873 ) , had a two - storey casemate . Single casemates ( 1889 onwards ) . A " casemate " was an armoured room in the side of a warship , from which a gun would fire . A typical casemate held a 6 - in gun , and had a 6 " front plate ( forming part of the side of the ship ) , with thinner armour plates on the sides and rear , with a protected top and floor , and weighed about 20 tons ( not including the gun and mounting ) . Casemates were similar in size to turrets ; ships carrying them had them in pairs : one on each side of the ship . The first battleships to carry them were the British " Royal Sovereign " class laid down in 1889 . They were adopted as a result of live - firing trials against HMS " Resistance " in 1888 . Casemates were adopted because it was thought that the fixed armour plate at the front would provide better protection than a turret , and because a turret mounting would require external power and could therefore be put out of action if power were lost - unlike a casemate gun , which could be worked by hand . The use of casemates enabled the 6 - in guns to be dispersed , so that a single hit would not knock out all of them . Casemates were also used in protected and armoured cruisers , starting with the 1889 " Edgar " class . and retrofitted to the 1888 " Blake " class during construction . In the pre - dreadnought generation of warships , casemates were placed initially on the main deck , and later on the upper deck as well . Casemates on the main deck were very close to the waterline . In the " Edgar " class , the guns in the main deck casemates were only above the waterline . Casemates that were too close to the waterline or too close to the bow ( such as in the 1912 " Iron Duke " - class dreadnoughts ) were prone to flooding , making the guns ineffective . Armoured vehicles . In regards to armoured fighting vehicles , casemate design refers to vehicles that have their main gun mounted directly within the hull and lack the rotating turret commonly associated with tanks . Such a design generally makes the vehicle mechanically simpler in design , less costly in construction , lighter in weight and lower in profile . The saved weight can be used to mount a heavier , more powerful gun or alternatively increase the vehicle ' s armour protection in comparison to regular , turreted tanks . However , in combat the crew has to rotate the entire vehicle if an enemy target presents itself outside of the vehicle ' s limited gun traverse arc . This can prove very disadvantageous in combat situations with no clearly drawn front line . During World War II , casemate tanks were heavily used by both the German Wehrmacht and the Soviet Red Army . They were mainly employed as tank destroyer s and assault gun s . Tank destroyers , intended to operate mostly from defensive ambush operations , did not need a rotating turret as much as offensively used tanks , while assault guns were mainly used against fortified infantry positions and could afford a longer reaction time if a target presented itself outside the vehicle ' s gun traverse arc . Thus , the weight and complexity of a turret was thought to be unnecessary , and could be saved in favor of more capable guns and armor . In many cases , casemate vehicles would be used as both tank destroyers or assault guns , depending on the tactical situation . The Wehrmacht employed several casemate tank destroyers designated as " Jagdpanzer " ( literally ' hunting tank ' ) . Examples are the Jagdpanzer IV , the Jagdtiger and the Jagdpanther ( the latter two translate as ' Hunting Tiger ' and ' Hunting Panther ' , respectively ) . Assault guns were designated as ' Sturmgeschütz ' , like the Sturmgeschütz III and Sturmgeschütz IV . In the Red Army , casemate tank destroyers and self - propelled guns bore an " SU - " or " ISU - " prefix , with the " SU - " prefix an abbreviation for Samokhodnaya Ustanovka , or " self - propelled gun " . Examples are the SU - 100 or the ISU - 152 . Both Germany and the Soviet Union mainly built casemate tanks by using the chassis of already existing turreted tanks , instead of designing them from scratch . While casemate tanks played a very important role in World War II ( the Sturmgeschütz III for example was the most numerously built armored fighting vehicle of the German Army during the entire war ) , they became much less common in the post - war period . Heavy casemate tank destroyer designs such as the US T28 and the British Tortoise never went beyond prototype status , while casemate vehicles of a more regular weight , such as the Soviet SU - 54 - 122 , saw only very limited service . The general decline of casemate vehicles can be seen in the technological progress which resulted in the rise of universal main battle tanks , which unified in them the capability to take up the roles and tasks which in the past had to be diverted between several different classes of vehicles . However , vehicles such as the German Kanonenjagdpanzer of the 1960s still let the casemate concept live on , while the Swedish Army went as far as employing a casemate tank design , the Stridsvagn 103 , or ' S - Tank ' , as their main armoured fighting vehicle from the 1960s until the 1990s , favoring it over contemporary turreted designs . Other casemate design ideas , such as the projected German Versuchsträger 1 - 2 with two main guns , were developed even later .