Very interesting!
« - VII-C Turm II: With installation on u-boats starting in December 1942, the turm II provided room for a second AA gun «
Small precision about this second room for AA gun:
Very few U-boot were equipped with a 4 guns turret AA (30mm i think) inside this second room.
For instance, U 333 of Cremer was equipped this way, and with twin AA 20mm in first room.
It was probably at the captain requirement though.