Operation Tiger

Operation Tiger was the code name for one in a series of large-scale rehearsals for the D-Day invasion of Normandy, which took place on Slapton Beach in Devon, England. Coordination and communication problems resulted in friendly fire deaths 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 946 American servicemen. The government didn't inform the families until after D-day and reported that that's where they died.