For other uses, see Blockhouse (disambiguation).
It usually refers to an isolated fort in the form of a single building, serving as a defensive strong point against any enemy that does not possess siege equipment or, in modern times, artillery, air force and cruise missiles.
However, a blockhouse may also refer to a room within a larger fortification, usually a battery or redoubt.
The term is of uncertain origin, perhaps related to Middle Dutch and 18th-century French (blockade).
In ancient Greece
Blockhouses existed in ancient Greece, for example the one near Mycenae.
Early blockhouses in England
Early blockhouses were designed solely to protect a particular area by the use of artillery, and they had accommodation only for the short-term use of the garrison.
The first known example is the Cow Tower, Norwich, built in 1398, which was of brick and had three storeys with the upper storeys pierced for six guns each.
Often sited in pairs, the blockhouses were not built to a common design, but usually consisted of a stone tower and bastion or gun platform, which could be semi-circular, rectangular or irregular in shape.
Coastal fortifications in Malta
Almost every battery and redoubt had a blockhouse, which served as gun crew accommodation and a place to store munitions.
Many of the batteries consisted of a semi-circular or polygonal gun platform, with one or two blockhouses at the rear.
The blockhouses usually had musketry loopholes, and in some cases were linked together by redans.
Many of the redoubts consisted of a pentagonal platform with a rectangular blockhouse at the rear, although a few had semi-circular or rectangular platforms.
A few of the redoubts consisted of a single tower-like blockhouse without a platform, and were known as tour-reduits.
Of the four tour-reduits that were built, only the Vendôme Tower survives today.
Age of exploration
Originally blockhouses were often constructed as part of a large plan, to "block" access to vital points in the scheme.
But from the Age of Exploration to the nineteenth century standard patterns of blockhouses were constructed for defence in frontier areas, particularly South Africa, New Zealand, Canada, and the United States.
If the structure was of timber, usually the upper storey would project outward from the lower so the upper storey defenders could fire on enemies attacking the lower storey, or perhaps pour water on any fires.
When the structure had only one storey, its loopholes were often placed close to the ceiling, with a bench lining the walls inside for defenders to stand on, so that attackers could not easily reach the loopholes.
Blockhouses were normally entered via a sturdy, barred door at ground level.
In some cases, blockhouses became the basis for complete forts, by building a palisade with the blockhouse at one corner, and possibly a second tower at the opposite corner.
Many historical stone blockhouses have survived, and a few timber ones have been restored at historical sites.
Second Boer War
Around 441 were solid masonry blockhouses, many of which stand today.
Different designs were used in the construction of these blockhouses, but most were either two or three story structures built using locally quarried stone.
However the vast scale of British strategy led the British to develop cheaper, double-skinned corrugated iron structures.
These could be prefabricated, delivered to site by armoured train, and then have locally sourced rocks or rubble packed inside the double skin to provide improved protection.
A circular design developed by Major Rice in February 1901 had good all round visibility, and the lack of corners did away with the need for a substructure.
Failure due to wood rot and splintering when hit by bullets or shrapnel were eliminated.
The steel door to the blockhouse was sheltered by another piece of corrugated iron.
The Major Rice blockhouse could be erected in six hours by six trained men.
With the change from square gabled roofs to a circular design, they were given the nickname "Pepperpot blockhouse".
With mass production the cost to build a blockhouse dropped down to £16, compared to several hundred pounds for masonry ones.
These blockhouses played a vital role in the protection of the railway lines and bridges that were key to the British military supply lines.
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.
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 sturdiest 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.
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.
During the Cold War the shelter was in use as a NATO foodstore.
In the Guerrilla phase of the Irish Civil War (1922–1923), a network of blockhouses was constructed to protect the railways from guerrilla attacks.
- Battery tower
- Blockhouse No. 1, New York City
- Blockhouse, Nova Scotia
- Block House in Claymont, Delaware
- British hardened field defences of World War II - Pillbox
- Fort King George in Darien, Georgia
- Fort Pitt Blockhouse in Point State Park in Pittsburgh
- Martello tower
- Sangar (fortification)
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Blockhouse.