Thank you very much for the info!

I did some more digging (well, "tried" would be a better word for it) and couldn't find any more info on this. Even Radermacher himself apparently only wrote that he was the commander of U5 in "März '43 (1 zg als Vertretung)". The short overview of his career by L. Zinnau (former crew member of U393) also states pretty much exactly what's written in the book you quoted. (unfortunately, I don't have the access to the book myself – I guess that's the curse of living in the middle of nowhere).

I'm still puzzled by those dates found on the archive's site (that say 'from 20.3.1943 – 25.3.1943'). I'm not surprised Radermacher's not listed anywhere on u-boat's papers as the commander, since it was only for a very short period, but where on earth did those exact dates come from? :/

Could I perhaps ask you for another favour, since you have the book about u-boat commanders at hand? Does it say anywhere, that A. Radermacher entered Bundesmarine in 1957 and later ended his career as Fregattenkapitän?

Thanks!