aerial photograph of Knock John Sea Fort, one of the Maunsell Forts built during World War II as anti aircraft defences. The towers contained the crew quarters and operational rooms while a pair of QF 3.75 inch anti-aircraft guns and ammunition storage were placed on the gun deck above. The structure was constructed ashore and then towed to its operational site for a controlled sinking into place. The fort was operational until 1945 and then abandoned after 1956, however the construction was so strong that the forts remain in good structural condition to this day.