air station spread out across Calshot Spit, including occupying the 1895 battery. Calshot's remaining guns were removed and probably dispatched to the front line in France. During the inter-war years Calshot was taken over by the Royal Air Force, becoming RAF Calshot. It was used as the School for Naval Co-operation and Aerial Navigation from 1918 onwards and began housing the Seaplane Training Squadron in 1931. The 1895 battery was demolished to create additional space for the growing station, and a narrow-gauge railway constructed along the spit. Parts of the castle moat were concreted over to provide parking for planes. Calshot twice hosted the Schneider Trophy air races over the Solent, the last two in the sequence of popular international events designed to encourage the development of new, high-speed technology. The Empire Air Day events were also held at Calshot, attracting 1,000 visitors in 1935. During the Second World War, Calshot Castle was initially defended by troops from the Hampshire Regiment, and a barge equipped with two anti-aircraft guns and a Bofors gun. Air-raid shelters were constructed in the castle's moat, with five boats from the base taking part in the Dunkirk evacuation. The threat of German invasion increased, however, and the defences were expanded in 1940, with two 12-pounder quick firing guns placed on the keep's roof, supported by searchlights. Two additional subordinate batteries, Bungalow and Stonepoint, were built the following year on the other side of Southampton Water and further south-west along the coast. The castle was not damaged during the war and by 1943 was placed on a "care and maintenance" basis, acting as a way station for passing aircraft. 1945–21st century After the war, Calshot returned to duty as an active air base, housing two squadrons of Sunderland flying boats which took part in the Berlin airlift of 1948, before being passed across to Maintenance Command in 1953. The Southampton Harbour Board built a coastguard lookout tower at the castle in 1952, and the following year they began to construct a signal station tower on top of the keep, complete with radar and radio facilities, which opened in 1958. By then, military seaplanes had become obsolete, and the RAF station was finally closed in 1961. Hampshire County Council leased the site from the Crown Estates in 1964; the castle itself passed into the guardianship of the state, and the hangars were used as an activity centre.