Exercise Tiger, or Operation Tiger, which took place in April 1944 on Slapton Sands in Devon, was one of a series of large-scale rehearsals for the D-Day invasion of Normandy. Coordination and communication problems resulted in friendly fire injuries during the exercise, and an Allied convoy positioning itself for the landing was attacked by E-boats of Nazi Germany's Kriegsmarine, resulting in the deaths of at least 749 American servicemen.[1][2]
Because of the impending invasion of Normandy, the incident was under the strictest secrecy at the time and was only minimally reported afterwards.