Under complete secrecy, Exercise Tiger began in December 1943. The area of Slapton in Devon was evacuated and it became the US military's D-Day training ground for 6 months. Most men didn't know the exact plans of D-day. Those who did were on a BIGOT list and had knowledge of the true dates and locations.
However, on 28 April 1944, an Allied convoy pracitising for the landings was attacked by the German Navy. It resulted in the deaths of 946 American servicemen. 10 men on the BIGOT list disappeared and fearing they had been captured by the enemy, the invasion was nearly called off. All their bodies were subsequently found. The disaster was kept secret and was rarely spoken about even after the war. As such it is known as 'forgotten'. Some families only started to learn the truth about what happened to their family members as late as the 1980s.