The U-boat, short for Unterseeboot ("Undersea boat"), was a type of military submarine operated by Germany during World War I and World War II. U-boats were efficient fleet weapons against enemy warships, but their most effective use was against Allied merchant shipping during the two wars. From 1939 to 1943, U-boats fought against the Allied Powers during the Battle of the Atlantic of World War II, sinking Allied merchant ships in periods known as "Happy Times". From 1942 onwards, Nazi Germany began to lose the Battle of the Atlantic when the "Enigma" code was cracked by British scientists led by Alan Turing, leading to the British intercepting U-boat wolfpacks and leading away their convoys. The German subs began to suffer heavy losses, and 60% of U-boat crewmen died during the war. In 1945, the last U-boats were surrendered to the Allied Powers, and the British scuttled captured U-boats during Operation Deadlight at the war's end.