Abunker is a defensive fortification designed to protect people and valued materials from falling bombs, artillery, or other attacks. Bunkers are almost always underground, in contrast toblockhouses which are mostly above ground.[1] They were used extensively inWorld War I,World War II, and theCold War for weapons facilities, command and control centers, storage facilities, etc. Bunkers can also be used as protection fromtornadoes.
Trench bunkers are small concrete structures, partly dug into the ground. Many artillery installations, especially forcoastal 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 withfiber-reinforced plastic shells. Bunkers deflect the blast wave from nearbyexplosions 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 theshock wave passes, and blockradiation.
A bunker's door must be at least as strong as the walls. In bunkers inhabited for prolonged periods, large amounts ofventilation orair conditioning must be provided. Bunkers can be destroyed with powerful explosives andbunker-bustingwarheads.
The wordbunker originates as aScots word for "bench, seat" recorded 1758, alongside shortenedbunk "sleeping berth".[2] The word possibly has aScandinavian origin:Old Swedishbunke means "boards used to protect the cargo of a ship".[3]In the 19th century the word came to describe acoal store in a house, or below decks in a ship. It was also used for asand-filled depression installed on a golf course as a hazard.[4]
In theFirst World War thebelligerents built underground shelters, calleddugouts inEnglish, while the Germans used the termBunker.[5][6] By theSecond World War the term came to be used by the Germans to describe permanent structures both large (blockhouses), and small (pillboxes), and bombproof shelters both above ground (as inHochbunker) and below ground (such as theFührerbunker).[7]The military sense of the word was imported into English during World War II, at first in reference to specifically German dug-outs; according to theOxford 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".[8] All the early references to its usage in the Oxford English Dictionary are to German fortifications. However, in theFar East the term was also applied to the earth and log positions built by the Japanese, the term appearing in a 1943 instruction manual issued by theBritish Indian Army and quickly gaining wide currency.[9]
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 opentrench and also include top protection against aerial attack. They also provide shelter against the weather. Some bunkers may have partially open tops to allow weapons to be discharged with the muzzle pointing upwards (e.g., mortars and anti-aircraft weapons).[10]
Many artillery installations, especially forcoastal 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 metres (11 ft) thick,[11] and an underground bunker was constructed for theV-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 fromaerial bombardment. Industrial bunkers are also built for control rooms of dangerous activities, such as 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.
When a house is purpose-built with a bunker, the normal location is a reinforced below-ground bathroom with large cabinets.[12] One common design approach usesfibre-reinforced plastic shells. Compressive protection may be provided by inexpensive earth arching.[citation needed] The overburden is designed to shield from radiation.[citation needed] To prevent the shelter from floating to the surface in high groundwater, some designs have a skirt held down with the overburden.[13] It may also serve the purpose of asafe room.[citation needed]
Large bunkers are often bought bysuper rich individuals in case ofpolitical instability, and usually store or access large amounts of energy for use. They are sometimes referred to as "luxury bunkers," and their locations are often documented.[14][15]
Munitions storage bunkers are designed to securely storeexplosiveordnance and contain any internal explosions. The most common configuration forhigh explosives storage is theigloo shaped bunker.[citation needed] They are often built into a hillside in order to provide additional containment mass.
A specialized version of the munitions bunker called aGravel Gertie is designed to containradioactive debris from an explosive accident while assembling or disassemblingnuclear warheads. They are installed at all facilities in the United States and United Kingdom which do warhead assembly and disassembly, the largest being thePantex plant inAmarillo, Texas, which has 12 Gravel Gerties.[16]
Bunkers deflect the blast wave from nearbyexplosions to prevent ear and internal injuries to people sheltering in the bunker. While frame buildings collapse from as little as 21 kPa (3 psi; 0.21 bar) ofoverpressure, bunkers are regularly constructed to survive over 1,000 kPa (150 psi; 10 bar). This substantially decreases the likelihood that abomb (other than abunker buster) can harm the structure.
The basic plan is to provide a structure that is very strong inphysical compression. The most common purpose-built structure is a buried, steelreinforced concretevault orarch. Most expedient 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 (3.5–6.5 ft), flexible tent of thin wood is placed in a deep trench, and then covered with cloth or plastic, and then covered with 1–2 m (3.5–6.5 feet) of tamped earth.
A large ground shock can move the walls of a bunker several centimeters in a few milliseconds. Bunkers designed for large ground shocks must have sprung internal buildings to protect inhabitants from the walls and floors.[17]
Nuclear bunkers must also cope with the underpressure that lasts for several seconds after theshock wave passes, and blockradiation. Usually, these features are easy to provide. The overburden (soil) and structure provide substantial radiation shielding, and the negative pressure is usually only1⁄3 of the overpressure.[18]
A bunker on the island ofTexel, in the Netherlands.
The doors must be at least as strong as the walls. The usual design is now starting to incorporatevault doors. 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.[citation needed] 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 ofventilation orair 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 theKearny Air Pump. Ventilation openings in a bunker must be protected byblast valves. A blast valve is closed by a shock wave, but otherwise remains open. One form of expedient blast valve is worn flat rubbertire treads nailed or bolted to frames strong enough to resist the maximum overpressure.[19]
Bunkers can be destroyed with powerful explosives and bunkerbusting warheads. The crew of apillbox can be killed withflamethrowers.[20] 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.
^Harry Horstmann,Der Soldat: In Sprache und Tradition (2010), p. 153.
^"DWDS – Bunker".Archived from the original on 16 November 2016. Retrieved16 November 2016. Das Wortauskunftssystem zur deutschen Sprache in Geschichte und Gegenwart
^"The German term Bunker was used to denote a type of shelter which was of permanent construction. It can be distinguished from the improvised type built in cellars or by reinforcing ordinary buildings. Bunkers were of two types: underground and tower" (Morale Division (1945).The effect of bombing on health and medical care in Germany. Reports: European war, United States Strategic Bombing Survey. Vol. 65 (2 ed.). United States War Department. p. 189 (footnote "*").)
^abWar Pictorial, cited after"bunker, n.1.c".Oxford English Dictionary (Second ed.). Oxford University Press. December 2011 [1989].(subscription required)
^Kearny, Cresson H (1987).Nuclear War Survival Skills. Oak Ridge National Laboratory.ISBN0-942487-01-X. Retrieved19 June 2008.NOTE: Kearny recommends stockpiling materials for a blast orfallout shelter and constructing it only if war appears very likely.
^"Bunker Thoughts".prepare-and-protect.net. 25 January 2014.Archived from the original on 30 September 2017. Retrieved2 May 2018.
^The Survival Option: Guide to Living Through Nuclear War, Ivan Tyrrell. Publisher: Jonathan Cape Ltd; 1st Edition (1982), Language: English, Hardcover: 256 pages,ISBN0224020595
