Bunkers

thumb|The Flak tower|Flakturm at the [[Augarten in Vienna. Flak towers were used as both above-ground bunkers and anti-aircraft gun blockhouses by Nazi Germany]] thumb|The north entrance to the Cheyenne Mountain Complex in [[Colorado, United States]] A bunker 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 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

thumb|A mid-19th century artillery casemate at Fort Knox (Maine)|Fort Knox, Maine.

type of submarine base that acts as a bunker to protect submarines from air attack

thumb|Examples of Regelbau designs that were used in the construction of the Neckar-Enz position The Regelbau (German for "standard(ised) construction") were a series of standardised bunker designs built in large numbers by the Germans in the Siegfried Line () and the Atlantic Wall as part of their defensive fortifications prior to and during the Second World War.