The topredoes used in the World Wars traveled at fifty knots, much faster than any ship, and they may be faster today. Then again, the homing topedo (like the guided missile) may have made speed less important than it was then.
The worst shark attack took place of a 7-day period in 1945 from July 30th to August 5th. The USS Indianapolis was on a covert mission delivering parts for the Atomic Bomds that ended the war. Since it was a secret mission, when a Japanese Topedo strucks it side, 1,100 of the 1,200 men crew went into the water and the US Navy, due to the secrecy of the mission, didn't know to look for the ship until it was a week overdue at port. Over the next week, sharks (great whites, hammerheads, oceanic white-tips, tiger sharks...) celebrated Thanksgiving by devouring more then 750 of the US Naval officers and sailors that entered the water on that fateful day. Sailors rescued from the water a week after the torpedo have estimated the number of sharks at over 1,000. That is the worst shark attack in history, bar none!