[Sailor Steve]

Yep, that pretty much sums it up. I always use magnetic up until I get the historic message to stop using them, then contact only until they give the message to use the new, improved magnetics.

Someone once posted a picture of them being changed, and it was definitely a physical procedure done outside the tube.

Depth and gyro settings were changed with a mechanical (later electric) device that fitted into a slot on the outside of the tube, but went right through to the torpedo inside. This is actually shown in the 'Uncut' version of Das Boot. Lining the fittings up was part of the reason it took so long to load the eels.