Yes, it's that big rounded kettle looking hatch.


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3rd pic down shows it open minus the hatch cover (based on pix of U 570)
2nd pic shows the closed hatch, altho not well (has two big arms, near the open torp loading bay). It was a spring loaded heavy hatch on a kettle not connected to interior (David Westwood has a cutawy I think in Anatomy of a U Boat)

I don't know how the shells were stored, tho - standing or on their side stacked? I'm trying to show shells being loaded, preparing for patrol. I might cheat and just have two guys handling the first shell to be stowed.