The submarines are XT-Craft, training versions of the X-Craft that attacked the Tirpitz in 1942. In 1946 two of these vessels were towed to Aberlady Bay and moored to a large concrete block, then used as target practice and gun tests by RAF aircraft. Afterward their badly damaged remains were simply left to rot (from www.undiscoveredscotland.co.uk/aberlady/aberladybay/index...).