SLAPTON SANDS, ENGLAND, NOV. 15 -- With tears, tributes and a bugler playing "Taps," the United States and Britain today finally honored 749 Americans killed in a rehearsal for the D-Day landings of World War II.

About 300 people prayed for the soldiers and sailors who perished off southwest England's Devon coast in the tragedy.

In driving rain overlooking the slate gray English Channel, Rep. Beverly Byron (D-Md.), whose late father, Capt. Harry C. Butcher, witnessed the maneuvers as Gen. Dwight D. Eisenhower's naval aide, and Peggy Verniquet, chairman of the local South Hams District Council, unveiled a plaque commemorating the deaths.

"May these men rest in the knowledge that the lessons in this tragedy added significantly to the ability of the Allies to carry out the successful invasion of Normandy on June 6, 1944," the plaque reads.

The ceremony ended a 16-year battle to gain official recognition for the young recruits who lost their lives the night of April 28, 1944, when "Exercise Tiger" turned into real combat. It started as a mock assault by 30,000 American troops, but turned real when nine German E-boats -- fast, light boats that harassed coastal waters -- torpedoed three amphibious landing craft. Hundreds were trapped and killed on the landing craft. Others died when some Americans fired on their own boats, thinking they were German.

Hundreds more dead were found the next morning, floating upside down because they put their life vests around their waists instead of under their arms.

Exercise Tiger marked one of the largest U.S. losses of life of any incident in the war to that point. Details were not made public until after the war.