Here's a freebie! Regards U-Boat action in WW1 against the Cunard liner,
Lusitania.
http://www.firstworldwar.com/features/lusitania.htm
(I DO kind of wonder about statements like, "...submerged and approached the large passenger liner at 9 knots," though! That'd make the old U-Boat faster than its WW2 counterparts!)