Exercise Tiger: Deadly D-Day Rehearsal

Exercise Tiger, or 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 Sands or Slapton Beach in Devon. 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 Germany's Kriegsmarine, resulting in the deaths of 946 American servicemen. Because of the impending invasion, the incident was under the strictest secrecy at the time and was only nominally reported afterward. As a result, Exercise Tiger has been called "forgotten."

In April 1944, Exercise Tiger proved to be a grisly rehearsal for the D-Day Invasion less than two months later.
One of the Largest, Most Ambitious Training Exercises Ever Conducted
This was not D-Day, June 6, 1944, the Allied landings on the Northern coast of France, the opening shots of the long-awaited second front in Europe, that great clash of arms in the titanic struggle against Hitler and his Nazi tyranny for the liberation of an enslaved Europe. This was not the invasion of Normandy; for that matter, it was not even Normandy. It was the east coast of England in late April 1944, a little more than a month before the real landings across the English Channel in German-occupied France.

This is the OFFICIAL website of Exercise Tiger Memorial Ltd
The roll of those who died
Memorial for the dead

Sonar images of the sunken D Day rehearsal ships