The War at Sea and in the Air
The German admiralty did not begin serious planning for a naval war against Britain until the winter of 1938 when, in a series of war games, it was revealed that there were too few U-boats for an effective submarine offensive. Admiral Dönitz was an experienced officer who had commanded a submarine in the First World War, ending up as a British prisoner-of-war when he had the misfortune to be forced to abandon his UB 68 after blowing a ballast tank in the middle of a British convoy. In 1935 Dönitz began working on the development of his 'pack' tactics (Rudeltaktik), whereby a group of medium submarines of type VII was to operate under a single commander. Dönitz estimated that for an effective offensive against British shipping in the Atlantic, at least 300 U-boats were needed. At the outset of the war the German navy only had 57 U-boats fit for service, of which only 23 were suitable for operations in the Atlantic.
Dönitz's proposals for a large increase in the number of U-boats were rejected by Admiral Raeder, the Commander-in-Chief of the German navy. Whereas Dönitz believed the German navy should concentrate on attacking Britain's merchant navy and thus sever Britain's overseas lifeline, Raeder believed that the objective should be the destruction of the Royal Navy. Hitler supported Raeder and told him that he had until 1946 to prepare the navy for a show down with the British. In line with this thinking the German admiralty (OKM) favoured a smaller number of larger submarines which were heavily armed and which had a longer range. Dönitz believed that this scheme, outlined in 'Plan Z', was fundamentally flawed in that it would take far too long to build a fleet that would be strong enough to take on the Royal Navy, whereas a crash programme of U-boat construction offered a viable alternative.