The largest-ever post-war salvage operation on Englandâs Thames River discovered seven shipwrecks up to 350 years old. They include the HMS London warship (blown up in 1665) a yacht converted to a Second World War gunboat, and a mystery wreck. A total of about 1,100 went down in the whole of the river. The salvage by Wessex Archaeology and the Port of London Authority was both historical and practical. The operation was filmed for the BBC and took four months, using a dozen divers who used 3D survey equipment to locate the wrecks in near-zero visibility in depth to 16 metres.