In both world wars, the German submarine fleet attempted to enforce a blockade on Great Britain, with the 
intention of starving the country into submission—and in both wars was prevented from doing so. The Kriegsmarine fleet suffered appalling losses during the Battle of the Atlantic, largely due to the skillful exploitation of enemy wireless traffic enciphered on the Enigma machine, along with Allied technical developments such as radar and sonar.The German Type XXI diesel submarine, brought into service at the end of the war, proved to be an exceptional weapon at the time, and its design was adopted as the basis of the Soviet Zulu and Whiskey classes, as well as the later Foxtrot class, the mainstay of the postwar Red Banner Fleet. Although noisy and easy to detect, a total of 75 Foxtrots were built before production ended in 1983. They were exported to India, Cuba, Libya, and Poland, and two were lost in accidents. The Foxtrot B-37 was lost in a torpedo explosion at Polnariy in 1962, and the B-33 sank off Vladivostok in 1991.