U-73 - Interesttingly To quote a nurse, Sheila Macbeth, " A BANG sent a shiver down the length of the ship." Britannic had either struck a mine, or taken a torpedo from U-73, she was in the area, and recently laid mines there.
Just before dawn on the 27th April 1916 the battleship H.M.S. Russell was on duty in the Mediterranean not far from Malta when, she struck two mines laid by the German submarine U73. The ship caught fire and sank; 124 of the crew were lost, but thankfully she sank close enough to Malta for many small boats to rescue 625 survivors.