British and later allied losses to the U-boats before 1944 were very large and, had Karl Dernitz had the additional 50 U-boats he wanted and, with British stocks of fuel usually only sufficient for two weeks, the war might well have been won by Germany very rapidly.
During the course of the Second World War, German U-Boats sank 2,282 merchant and 175 Naval ships. In May 1994, British cryptologists had deciphered the codes used by the German Enigma machine used for communications between submarines and their bases and, in that month alone and using other technologies, 44 U-boats were sunk. Subsequently a policy of chasing U-boats once contact had been made until they were destroyed meant that only one out of every ten submarines would return from patrol. Indeed, allied authorities were concerned that if all possible U-boats were intercepted, the Germans would be alerted to the fact that the allies were deciphering Enigma messages.
Despite the heavy losses, there was no shortage of volunteers to crew U-boats. Of some 39,000 men who volunteered U-boat service, 28,900 were killed at sea.
The germans intoduced the snorkel which allowed their U-boats to travel submerged while being able to obtain air and vent exhaust gases above the water. Improvements in allied radar soon allowed the location of the snorkels themselves.
