Bunker A bunker is a defensive military fortification designed to protect the inhabitants from falling bombs or other attacks . Bunkers are mostly below ground , compared to blockhouse s 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 explosion s 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 doors 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 bunkerbusting warheads . The crew of a pillbox can be killed with flamethrower s . Etymology . Bunker is a relatively recent addition to the English language to describe a military structure . According to the Oxford English Dictionary it is a " A military dug - out ; a reinforced concrete shelter " and its first use was 13 October 1939 " A Nazi field gun hidden in a cemented ' bunker ' on the Western front " ( War Pictorial ) . The word is German in origin and was used by the Germans to describe bombproof shelters both above ground as in " Hochbunker " and below ground as in the " Führerbunker " . 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 . Types . Trench . 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 ( grenade s , mortar shells ) . They also provide shelter against the weather . The front bunker of a trench system usually includes machine gun s or mortars and forms a dominant shooting post . The rear bunkers are usually used as command post s or Tactical Operations Center s ( TOCs ) , for storage and as field hospitals to attend to wounded soldiers . Artillery . 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 . Industrial . 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 . Personal . When a house is purpose - built with a bunker , the normal location is a reinforced below - ground bathroom with large cabinets . One common design approach uses fibre - reinforced plastic shells . Compressive protection may be provided by inexpensive earth arching . The overburden is designed to shield from radiation . To prevent the shelter from floating to the surface in high groundwater , some designs have a skirt held - down with the overburden . It may also serve the purpose of a safe room . Design . Blast protection . Bunkers deflect the blast wave from nearby explosion s to prevent ear and internal injuries to people sheltering in the bunker . While frame buildings collapse from as little as 3 psi ( 0 . 2 bar ) of overpressure , bunkers are regularly constructed to survive several hundred psi ( over 10 bar ) . This substantially decreases the likelihood that a bomb ( other than a bunker buster ) can harm the structure . The basic plan is to provide a structure that is very strong in physical compression . The most common purpose - built structure is a buried , steel reinforced concrete vault or arch . Most expedient ( makeshift ) blast shelters are civil engineering structures that contain large buried tubes or pipes such as sewage or rapid transit tunnels . Improvised purpose - built blast shelters normally use earthen arches or vaults . To form these , a narrow ( 1 - 2 metre ) flexible tent of thin wood is placed in a deep trench ( usually the apex is below grade ) , and then covered with cloth or plastic , and then covered with 1 – 2 metres of tamped earth . A large ground shock can move the walls of a bunker several centimetres in a few milliseconds . Bunkers designed for large ground shocks must have sprung internal buildings to protect inhabitants from the walls and floors . Nuclear protection . Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shock wave passes , and block radiation . Usually these features are easy to provide . The overburden ( soil ) and structure provide substantial radiation shielding , and the negative pressure is usually only 1 / 3 of the overpressure . General features . The doors must be at least as strong as the walls . The usual design is a trap - door , to minimize the size and expense . To reduce the weight , the door is normally constructed of steel , with a fitted steel lintel and frame . Very thick wood also serves , and is more resistant to heat because it chars rather than melts . If the door is on the surface and will be exposed to the blast wave , the edge of the door is normally counter - sunk in the frame so that the blast wave or a reflection cannot lift the edge . A bunker should have two doors . Door shafts may double as ventilation shafts to reduce digging . In bunkers inhabited for prolonged periods , large amounts of ventilation or air conditioning must be provided in order to prevent ill effects of heat . In bunkers designed for war - time use , manually operated ventilators must be provided because supplies of electricity or gas are unreliable . One of the most efficient manual ventilator designs is the Kearny Air Pump . Ventilation openings in a bunker must be protected by blast valve s . A blast valve is closed by a shock wave , but otherwise remains open . One form of expedient blast valve is tyre - treads nailed or bolted to frames strong enough to resist the maximum overpressure . If a bunker is in a built - up area , it may have to include water - cooling or an immersion tub and breathing tubes to protect inhabitants from fire storms . Bunkers must also protect the inhabitants from normal weather , including rain , summer heat and winter cold . A normal form of rainproofing is to place plastic film on the bunker ' s main structure before burying it . Thick ( 5 - mil or 0 . 13 mm ) , inexpensive polyethylene film serves quite well , because the overburden protects it from degradation by wind and sunlight . Countermeasures . Bunkers can be destroyed with powerful explosives and bunkerbusting warheads . The crew of a pillbox can be killed with flamethrower s . Complex , well - built and well - protected fortifications are often vulnerable to attacks on access points . If the exits to the surface can be closed off , those manning the facility can be trapped . The fortification can then be bypassed . Famous installations . Famous bunkers include the post - World War I Maginot Line on the French eastern border and Czechoslovak border fortifications mainly on the northern Czech border facing Germany ( but to lesser extent all around ) , Fort Eben - Emael in Belgium , Alpine Wall on the north of Italy , World War II Führerbunker , the V - weapon installations in Germany ( Mittelwerk ) & France ( e . g . La Coupole , and the Blockhaus d ' Éperlecques ) and the Cold War installations in the United States ( Cheyenne Mountain , Site R , and The Greenbrier ) , United Kingdom ( Burlington ) , Sweden ( Boden Fortress ) and Canada ( Diefenbunker ) . The Soviet Union maintained huge bunkers ( one of the secondary uses of the very deeply dug Moscow Subway system was as nuclear shelters ) . A number of facilities were constructed in China , such as Beijing ' s Underground City and Underground Project 131 in Hubei ; in Albania , Enver Hoxha dotted the country with hundreds of thousands of bunkers .