How did a rehearsal for D-Day on a sleepy stretch of the Devon coast turn into a bloodbath resulting in the death of hundreds of Allied soldiers? 'Exercise Tiger' was the Allies' worst training disaster of the 20th century - a combination of allied incompetence and enemy infiltration that was hushed up until 1984. Survivor and eye-witness accounts, top-secret documents, film archive and findings from underwater excavations help to reveal the secrecy and conflicting evidence that persists to this day.