Raymic1
Thank you for the good wishes, going on 92 takes its toll but I guess I should`t complain. Making a survey of all the modifications and years on the VIICs
would probably be a task for a historian rather than an engineer, in fact the development of the VII class has been a continious process from the very beginning. However
if we concentrate on the step from the first ordinary VIIC to the VIIC/41 you are right, the increased max. crush depth was the main thing. This was achieved by increasing the steelplate thickness particulary in the tower and controlroom area. This of course influenced the deplacement which implied a reduction of weigth. The weight reduction was obtained by doing a lot of modifications in the engineroom. By making the diesels nonreversible the heavy reversing mechanism was removed, the most visible item is the vertical reversingcylinder on top of the engine, up front. Then likewise the lubeoil purification plant. By introducing the non reversible dieselengine the surface maneuvring had to be substituted by a simpler main switch board. The switch board on all our VIICs ( ex U 995, U-926 and ex. U 1202 were all alike as all the main engines were the same. The U-995 had quite significant flare, ( Atlantic bow), the other less. Contrary to many images the U 995, U 926 and U 1202 had a ringfloat air valve on top of the snorkel mast, not the hinged type as on the museum U 995 today. As you might see there are a lot of minor differences within the VIIC class, some time you have the feeling that several yards made, within limits, their own design, particularly in the latter part of WW2. U 995 never operated with snorkel in WW2, in fact she was at the yard installing the snorkel at the surrender.
Feel free to ask further questions.
Tore