At the ripe old age of 21 years, my father spent his Christmas eve, 1944 aboard the SS Leopoldville as it made its way from Southampton to Cherbourg. He had trained to be an Army Airforce pilot, but he and all of his classmates had been washed out when they could supply no planes for them to fly.
Just shy of 6:00PM a single German U-boat torpedo struck the Leopoldville dead amidships. Of the 2,235 American servicemen on board, approximately 515 are presumed to have gone down with the ship. Another 248 died from injuries, drowning, or hypothermia. An unknown number of British soldiers died. Documents about the attack remained classified until 1996. Only a half-dozen other members of his company survived.
A complete account can be found here:
http://ahoy.tk-jk.net/macslog/BelgianTrooperSSLeopoldvi.html