Built by Henry VIII in 1539, for over 400 years the Castle remained a fully manned artillery base.
Calshot Naval Air Station opened in 1913 and during the First World War, Calshot provided Channel defence and a training base for pilots. In 1929 and 1931, Calshot was the venue of the famous Schneider Cup Trophy race. Calshot played an important role in the Second World War and became home to the Sunderland Flying Boat. After a long, chequered military history, RAF Calshot closed in 1961.
Today Calshot Castle is part of the Hampshire County Council-run Calshot Activities Centre.
At the entrance of the Southampton Water from the Solent is another of the blockhouse forts of Henry VIII., built in 1540 to command this entrance, at the same time as Hurst Castle, from which it is distant 14 miles. It was originally upon a small island until early in the eighteenth century, when the action of the tides closed the dividing channel. Leland calls it “a strange, late buildid castelle, caullid Caldshore, communely Cawshot”. It is a circular tower of two storeys, and a platform, surrounded by a low circular gun terrace with the battery, having the dwellings in rear; there are gun embrasures almost all round the tower. (Castles Of England, Sir James D. Mackenzie, 1896)