Blockhouse - Concrete Blockhouses

Concrete Blockhouses

During World War I and World War II, many types of blockhouses were built, when time allowed usually constructed of reinforced concrete. The major difference between a modern blockhouse and a bunker is that a bunker is constructed mostly below ground level while a blockhouse is constructed mostly above ground level.

Some blockhouses like those constructed in England in 1940 were built in anticipation of a German invasion, they were often hexagonal in shape and were called "pillboxes". About 28,000 pillboxes and other hardened field fortifications were constructed of which about 6,500 still survive.

In London the Admiralty Citadel is one of the most sturdy above ground structures built during World War II. It was constructed in 1940–1941 as a bomb-proof operations centre for the Admiralty, with foundations nine metres deep and a concrete roof six metres thick. It too was intended to serve as a strongpoint in defending against the feared invasion.

In Berlin and other cities during World War II some massive blockhouses were built as air-raid shelters and anti-aircraft artillery platforms. They were called Hochbunker (literally, "high bunkers"; better translated as 'above ground bunkers', to distinguish them from the usual deep i.e. underground air raid shelters) and those that functioned as anti-aircraft artillery platforms were also called Flak towers. Some were over six stories high; several survive to this day because of the high cost of demolition. The Pallasstrasse air-raid shelter in Berlin-Schöneberg has a post-war block of flats built over it. During the Cold War the shelter was in use as a NATO foodstore.

In the Guerrilla Phase of the Irish Civil War (1922–23) - a network of blockhouses was constructed to protect the railways from guerrilla attacks.