I just love these old school visualisations: here are all the ships lost by the British Navy during World War II. Many of these were hunted down by Nazi U-Boats. It's a staggering amount but it could have been a lot worse.
Thankfully, the good guys cracked the Nazi Enigma encrypting machine and, as a result, the Allies neutralised the Kriegsmarine's submarine fleet.
For comparison, the inset graphic on the bottom right shows the ships lost during World War I. [Longstreet—Thanks Jim!]