Hello RB,

Thanks for your gentle put-down. My sources are located in the depth of my memory, which was fed 50 plus years ago by Naval Intelligence reports (SNIPS) and other information which came to me during the evolution of tactics to be used against the type XXI. (By Aug 44, HMSub Seraph had been modified to simulate type XXI performance and was used for tactical development and training). I accept that memory over half a century or so is not infallible, I understand, but have not checked, that there may be some references in;
Doenitz, Memoirs: pp128, 236, 265, 253.
Rossler, The U-boat: pp 168-182, 208.
British Intelligence in WW2, Vol III, Part 1, HMSO 1984: pp238.

Would you support the thought that the type XXI programme drew so many captains and experienced crews from the front line boats that it diminished the effectiveness of the U-boats from D-day onwards? Apart from exceptions such as U486 and in spite of the advantage offered by the T5 Gnat torpedo and the Snorkel, very little success was achieved for the loss of some 90 boats in European waters. Only one type XXI reached active service out of some 120 commissioned.