rgued that 300 U-boats were needed to wage war against England, but he was overruled. Under Raeder's 1939 Z Plan, 249 U-boats, including 162 ocean-going ones, were to be constructed by 1948, a timetable which was based on Hitler's assurances to Raeder that war with the West would not begin before 1943.
Operations (1939-1940). Because of the small number of U-boats, they were used singly, mostly in the waters surrounding Great Britain where a number of isolated but stirring victories were recorded in 1939. All told, U-boats and mines laid by them sunk about 320,000 tons in the last four months of 1939 but only an average of about 50,000 tons a month during the first quarter of 1940 (Terraine 226-227).The lethality of U-boat attacks increased after Nazi Germany gave orders in January 1940 that ships were to be sunk without warning. The acquisition in July 1940 of French Atlantic ports expanded by several thousand miles the cruising range of U-boats. During the Norwegian campaign in April 1940, B-Dienst, the Kriegsmarine's signal service, began reading British coded naval ciphers. According to Hughes, "Donitz more often than not had precise advance information about where to concentrate his forces" against Allied convoys (72).
The British, too, entered World War II unprepared to counter large-scale submarine attacks. In the last seven months of 1940 Donitz took advantage of British weakness by launching a sustained U-boat offensive, the main brunt of which Hughes said "fell on the merchant shipping in the Western Approaches [to Britain] which had only forty escorts and a handful of armed merchant cruisers to protect it" (80). The result was nearly 750,000 in lost tonnage due to U-boat sinkings in June-August, as compared with a little over 150,000 in the preceding three months (Hughes 305).
Armed raiders and other surface ships scored some successes on the high seas, but suffered some catastrophic losses, especially the sinking ...