Fort Blockhouse

Fort Blockhouse is a former military establishment in Gosport, Hampshire, England, and the final version of a complicated site. At its greatest extent in the 19th century, the structure was part of a set of fortifications which encircled much of Gosport. It is surrounded on three sides by water and provides the best view of the entrance to Portsmouth Harbour. As HMS Dolphin, the fort was for most of the 20th century the home of the Royal Navy Submarine Service. It is unique in that it was built over five centuries from its original construction as a blockhouse in 1431 to the final addition of submarine base structures in the mid-1960s. Coastal fortification was abolished nationally in 1956 and the submarines left in the 1990s.

Fort data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).