There were 8 pressure hull sections and 2 end plates in the Type VII C U-Boat design of the pressure hull and the thickness differed from section to section. Starting at the stern: (frame 0) the Aft curved end plate is 35 mm thick, section 1 (aft torpedo room area) is 16 mm thick (frame 0 - 12) length 6000 mm, section 2 is 17 mm thick (frame 12 - 18 approx.) length 3500 mm, section 3 is 17.5 mm thick (frame 18 approx. - 27.5) length 5500 mm, section 4 is 18 mm thick (frame 27.5 - 36 approx.) length 7100 mm, section 5 (control room) is 18.5 mm thick (frame 36 approx. - 50.5) length 9100 mm and the tower curved top plate is 22 mm thick because of multiple openings and the top plate is welded to the tower walls which are 22 mm thick, section 6 is 18 mm thick (frame 50.5 - 62.5) length 7200 mm, section 7 is 17.5 mm thick (frame 62.5 - 75.5) length 7900 mm, and section 8 (forward torpedo room area) is 16 mm thick (frame 75.5 - 81) length 3100 mm and assuming the bow curved end plate is 35 mm thick (frame 81). A larger diameter section requires a heavier steel plate for the pressure hull.

The Type VII C design was subjected to a weight loss program by using lighter machinery wherever possible, and lighter electrical components (i.e., the e-motor rotary switchboard control panel replaced the heavier toggle switchboard control panel). The results were a weight reduction of 11.5 tons which meant they could increase the thickness of the pressure hull in the Type VII C by 10 tons. For example; the control room hull thickness was increased from 18.5 mm to 22 mm. The test diving depth (60% of the crush diving depth) increased from 150 m to 180 m, and the destruction diving depth increased from 250 m to 300 m.

Scott