Hi Ron C.,
Location of my sources mostly like yours. Lately more often than I care for, I discover localised \"Swiss cheese syndrome\" in my \'primary\' sources as well. :-))
Your questions re experience of front line boats is a rather interesting one. Here are my thoughts on the the subject (short version):
First, it is quite clear that the learning curve of Uboat commanders and crews after summer/fall \'43 was quite a bit \"shorter\" than before. Experienced commanders had already been transferred to shore duties or were POW\'s or dead.
Years ago I accepted the premise, that the transfer of personell to the XXI building program contributed to the slaughter of the front line type 7\'s and 9\'s. I am now convinced, the primary reason is the tremendous improvements of the Allied\'s anti-sub warfare capabilities the year before. Secondary, the German persistence to prosecute the attack with now obsolete equipment. Relative crew inexperience was at best a tertiary reason.
If you look though the list of really known names like Schnee, Topp etc., they were out of the front boats over a year before. Also, these fellows got their XXI\'s through the training periods after commissioning faster than the average 6-7 months.
The Zaunkoenig T5 (=Wren, not Gnat) was practically checkmated by the \"Geraeuschbojen\" towed by Allied escorts. Pretty good intelligence work ensured those towed buoys to be aboard the escorts practically at the same time, when the first T5\'s were delivered to the boats. Only the T11 (Geier = Vulture) was able to ignore the buoys and go for the sounds of the ship.
I am amazed about the very quick modification of HMS Seraph. After all, that was only a couple of months after commisioning of the frisr XXI. Do you recall the changes made?