Hi, Each commissioned U-boat had its own number, in some cases the same number was used by more than one U-boat, this presumably being if the first boat had been lost or de-commissioned thus making the number available for reuse. Although looking at the some periods listed in the Axis History site this is not always clear. My question concerns two boats, U3516 and U3517, both commissioned on 18.12.44 and 22.12.44 respectively at the same yard, but both are listed as having M-49 683 as their Feld post number, was there any reason for this as both survived until 02.05.45. John