A bunker is a defensive military fortification. Bunkers are mostly below ground, compared to blockhouses which are mostly above ground. They were used extensively in World War I and World War II on a tactical level, while during the Cold War, massive bunker complexes were built to house both strategic (command & control) infrastructure as well as government personnel and stores for the event of a nuclear war.
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 Center (TOC), for storage and as field hospitals to attend to wounded soldiers.
A trench near La Boisselle during the Battle of the Somme
Dug-in guard posts (with loopholes through which to fire guns) and made from concrete are also known as ‘pillboxes’. The originally jocular name arose from their perceived similarity to the cylindrical boxes in which medical pills were once sold. They are in effect a trench firing step hardened to protect against small-arms fire and grenades and raised a little to improve the field of fire.
A WW2 pillbox on the East coast of England (the railings are a modern feature)
Many artillery installations, especially for naval 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. Since artillery bunkers were often constructed for very large guns in a pre-defined location and as part of a larger system of defenses (such as for a port town or a seacoast), they are amongst the largest individual pre-Cold War bunker types found. The walls of installations like the ‘Batterie Todt’ in northern France were up to 3.5 m thick, with the gun inside capable of reaching over the English Channel to the opposite coast.
German bunkers at Longues-sur-Mer in France
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.
Inside the Chowder Bay Bunker