Dönitz and Raeder accepted the death of the Z Plan upon the outbreak of war. The U-boat programme would be the only portion of it to survive 1939. Both men lobbied Hitler to increase the planned production of submarines to at least 29 per month. The immediate obstacle to the proposals was Hermann Göring, head of the Four Year Plan, commander-in-chief of the Luftwaffe and future successor to Hitler. Göring would not acquiesce and in March 1940 Raeder was forced to drop the figure from 29 to 25, but even that plan proved illusory. In the first half of 1940, two boats were delivered, increased to six in the final half of the year. In 1941 the deliveries increased to 13 to June, and then 20 to December. It was not until late 1941 the number of vessels began to increase quickly. From September 1939 through to March 1940, 15 U-boats were lost—nine to convoy escorts. The impressive tonnage sunk had little impact on the Allied war effort at that point.