by HMS Uplifter. Divers later established that the foundations were solid, but in a later storm the fort took on a 15 degree list. In the mid-1960s under-scouring had further distorted the fort: large holes had appeared in east leg, sea water had flooded the lower levels and the platform had become detached with huge gaps between the deck. Tongue Sands Fort finally collapsed into the under-scouring hole during storms on 21/22 February 1996, leaving only a single 18 foot stump of the south leg remaining visible above sea level. Knock John Fort (U4) Knock John fort is situated approximately from the coast off Essex and was grounded on 1 August 1942. It was decommissioned on 14 June 1945 and evacuated on 25 June 1945. The platform was maintained until May 1956 when it was abandoned. In 2009, it was observed that there was a slight distortion of the legs when viewing the tower from west to east. It is thought that underscouring is the cause of this. Maunsell army forts Maunsell also designed forts for anti-aircraft defence. These were larger installations comprising seven interconnected steel platforms. Four towers arranged in a semicircle ahead of the control centre and accommodation each carried a QF 3.7-inch gun, a tower to the rear of the control centre mounted Bofors 40 mm guns, while the seventh tower, set to one side of the gun towers and further out, was the searchlight tower. Three forts were placed in Liverpool Bay: Queens AA Towers Formby AA Towers Burbo AA Towers and three in the Thames estuary: Nore (U5), Red Sands (U6) Shivering Sands (U7) The Mersey forts were constructed at Bromborough Dock, the Thames forts at Gravesend. Proposals to construct Forts off the Humber, Portsmouth & Rosyth, Belfast & Londonderry never materialized. During World War II, the Thames estuary forts shot down 22 aircraft and about 30 flying bombs; they were decommissioned by the Ministry of Defence in the late 1950s. Nore Fort (U5) Nore fort was the only one built in British territorial waters at the time it was established. Other forts were in international waters until the three-mile limit was extended to . The fort was badly damaged in 1953 during a storm, then later in the year a Norwegian ship, Baalbek, collided with it, destroying two of the towers, killing four civilians and destroying guns, radar equipment and supplies. The ruins were