Exercise Tiger , a training mission for D - Day , took place in June 1944 . ( CNN ) -- More than 700 American servicemen lost their lives in German torpedo boat attack . New sonar images show the sunken ships in the English Channel . Operation Tiger revealed some problems that were fixed before actual D - Day landings .
Exercise Tiger , a training mission for D - Day , took place in June 1944 . More than 700 American servicemen lost their lives in German torpedo boat attack . New sonar images show the sunken ships in the English Channel . Operation Tiger revealed some problems that were fixed before actual D - Day landings .