At the outbreak of World War II, Cramond Island, along with other islands in the Forth, was refortified and armed with two 12-pdr guns, and a modern 6-pdr twin equipment, designed specifically to tackle fast-moving torpedo boats. An anti-submarine net and anti-boat boom was laid across the estuary from Cramond Island directly to Inchcolm, and then to the Charles Hill battery on the Fife coast. The barrier was to protect ships in the anchorage from attack by torpedo boats, and to stop submarines entering the anchorage to attack shipping or to damage the dock gate of Rosyth Dockyard. The line of concrete pylons was built from Cramond Island to the shore to complete the anti-boat barrier (which is often misidentified as an anti-submarine barrier - the water is far too shallow). After crossing the causeway, the first structures are the emplacements for a 75 mm gun and its associated searchlight. Several WW2 buildings survive, including the housings for Coast Artillery Search Lights, stores, shelters and gun emplacements, as well as two engine rooms that once contained all the equipment necessary to supply power to the military installations on the island. The anchor points for the anti-submarine net and anti-boat boom are visible at the north end of the island at low tide.