A bunker is a defensive military fortification designed to protect people or valued materials from falling bombs or other attacks. Bunkers are mostly underground, compared to blockhouses which are mostly above ground They were used extensively in World War I, World War II, and the Cold War for weapons facilities, command and control centers, and storage facilities (for example, in the event of nuclear war). Bunkers can also be used as protection from tornadoes. Trench bunkers are small concrete structures, partly dug into the ground. Many artillery installations, especially for coastal artillery, have historically been protected by extensive bunker systems. Typical industrial bunkers include mining sites, food storage areas, dumps for materials, data storage, and sometimes living quarters. When a house is purpose-built with a bunker, the normal location is a reinforced below-ground bathroom with fibre-reinforced plastic shells. Bunkers deflect the blast wave from nearby explosions to prevent ear and internal injuries to people sheltering in the bunker. Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shock wave passes, and block radiation. A bunker's door must be at least as strong as the walls. In bunkers inhabited for prolonged periods, large amounts of ventilation or air conditioning must be provided. Bunkers can be destroyed with powerful explosives and bunker-busting warheads The word bunker originates as a Scots word for "bench, seat" (recorded 1758, alongside shortened bunk "sleeping berth"),perhaps cognate with bank, bench, and possibly by Scandinavian influence (Old Swedish bunke means "boards used to protect the cargo of a ship").A sense of "earthen seat" is recorded 1805 from whence the technical use in golf (by 1824). The word entered Dutch and German as a loanword from English in the 19th century, in the nautical sense of "room for coal storage in a ship". In German, the word came to be applied for dug-out military shelters in the World War I period. and came to be used by the Germans to describe bombproof shelters both above ground as in Hochbunker and below ground as in the Führerbunker. The military sense of the word was re-imported into English during World War II, at first in reference to specifically German dug-outs; according to the Oxford English Dictionary, the sense of "military dug-out; a reinforced concrete shelter" is first recorded on 13 October 1939, in "A Nazi field gun hidden in a cemented 'bunker' on the Western front". All the early references to its usage in the Oxford English Dictionary are to German fortifications. By 1947 the word was familiar enough in English that Hugh Trevor-Roper in The Last Days of Hitler was describing Hitler's underground complex near the Reich Chancellery as "Hitler's own bunker" without quotes around the word bunker This type of bunker is a small concrete structure, partly dug into the ground, which is usually a part of a trench system. Such bunkers give the defending soldiers better protection than the open trench and also include top protection against aerial attack (grenades, mortar shells). They also provide shelter against the weather. The front bunker of a trench system usually includes machine guns or mortars and forms a dominant shooting post. The rear bunkers are usually used as command posts or Tactical Operations Centers (TOCs), for storage and as field hospitals to attend to wounded soldiers. Many artillery installations, especially for coastal artillery, have historically been protected by extensive bunker systems. These usually housed the crews serving the weapons, protected the ammunition against counter-battery fire, and in numerous examples also protected the guns themselves, though this was usually a trade-off reducing their fields of fire. Artillery bunkers are some of the largest individual pre-Cold War bunkers. The walls of the 'Batterie Todt' gun installation in northern France were up to 3.5 m thick, and an underground bunker was constructed for the V-3 cannon. Typical industrial bunkers include mining sites, food storage areas, dumps for materials, data storage, and sometimes living quarters. They were built mainly by nations like Germany during World War II to protect important industries from aerial bombardment. Industrial bunkers are also built for control rooms of dangerous activities, e.g. tests of rocket engines or explosive experiments. They are also built in order to perform dangerous experiments in them or to store radioactive or explosive goods. Such bunkers also exist on non-military facilities.

• published: 11 Apr 2016
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