Informatiom on the amphibious accident off the coast of England during World War 11. It was training excerise for the D-Day landings?

I think you are referring to Slapton Sands in April 1944 and the rehearsal for the Utah Beach landings code named 'Operation Tiger'. This ended with the loss of nearly 1,000 lives following a lightening attack on the exercise by E-Boats operating out of Cherbourg. Ken Small 'The Forgotten Dead' is a book about the recovery of the Sherman Tank that now stands as a War Memorial at Slapton sands. A splendid read about the dedication of one man to uncover the truth. The site was chosen, in 1944, to replicate the beach landing and the inundated area that lies between the beach & land, which the US forces would then arrive at in France.