Hi Adam, I would think the number would be high, once war had been declared and the U-boat building programme began to increase the fleet numbers, the pre war U-boat I WO and II WO's and some NCO's, after passing U-Commander training had been allocated new boats, as well as replacing losses, then as the demand to appoint commanders for the increasing numbers of newly built boats outgrew the numbers of qualified officers with WO experience readily available, new men had to be found from somewhere. BdU, alert to this problem accordingly searched for any suitable officers. With the 'Fame & Glory' the U-boat arm was achieving new officer candidates, where ever they was serving in the armed forces, could either ask to be transferred to the U-boat arm, or, if they showed potential, be drafted. I expect the latter happened more and more later in the war as losses grew. Another example of what you are stating being Kpt G.Hessler (U107), he had served on the torpedo boat Falke before transferring, where he had U-boat training from 4/40 - 7/40, then CO training 8/40 - 9/40, going straight on to command U107 without any WO experience. The book German U-boat Commanders of World War II (ISBN 1-557500045-2), gives the career details of each CO, may assist you. Regards John