A documentary by Matt Richards that recalls a catastrophic WWII training exercise that resulted in the loss of hundreds of lives. Allied preparations for the D-Day landings included a mock invasion at Slapton Sands on the south Devon coast on 27 April 1944, complete with shelling of the beach by a British cruiser firing live ammunition. A breakdown in communications meant that American troops landed on the beach as the bombardment was taking place. Even worse, the following day a convoy of troop carriers was attacked by German E-boats. The terrible events of those two days were effectively hushed up and decades would elapse before the horror of Slapton was revealed. Even today, the total number of casualties remains uncertain. Accounts from survivors, top-secret documents, film archive and findings from underwater excavations combine in this moving film to reveal the secrecy and conflicting evidence that persist to this day.