Exercise Tiger was a rehearsal for the Utah Beach landing held at the Slapton Sands beach in Slapton, South Devon. Early in the morning of 28 April, 1944, German E-boats sighted a convoy of 8 LSTs in Lyme Bay and attacked. 638 servicemen were killed - 441 U.S. Army and 197 U.S. Navy personnel. Many drowned while waiting to be rescued.
Check
here for more info.