The possibility of developing a new type of U-boat was first mentioned to Hitler on 13 November 1941. In the early stages of experiment, the Naval Staff did not think it necessary to refer the subject to him again until 28 September 1942, when the need for a U-boat with increased underwater speed had been underlined by the defeat of the old U-boats, and when experimental production could at last be considered. Hitler then gave full support to the idea, and complete freedom to Raeder to take all decisions concerning experimental and mass production. But it was already obvious, as Raeder announced on 22 December 1942, that the new type could not be operational in any numbers until 1944 at the earliest; and on 8 July 1943 Doenitz, Raeder's successor, made it obvious that further difficulties had emerged and had led to the abandonment of the original models.

He told Hitler that new designs for an ‘electro-submarine’ with an under-water speed of 19 knots, a surface speed of 15 knots and a fish-like shape (some of these details being added by Doenitz on 19 January 1944) had been completed, and that they retained only the hull of the ‘Walter’ design, the model with which the original experiments had been conducted. He added that ‘in comparison with the Walter boats, the new type had the additional advantage of being able to recharge batteries and thus extend its endurance’; recommended that production should be switched to this newest type; and announced that, though he himself regarded it as too pessimistic, the Naval Staff's estimated date for the completion of the first of the boats was November 1944. Hitler expressed his complete agreement and ordered Speer to give top priority to the programme.

The renewed failure of the old-type U-boats, when they returned to the Atlantic in September 1943, confirmed, as Doenitz said on 26 February 1944, that ‘our general tendency to change over to the new-type U-boat and under-water tactics is correct in every respect’; and that failure, leading Hitler and Doenitz to put all their hopes in the Atlantic on the emergence of the new boats, was enough to ensure that all possible emphasis was kept on their development.