Hi, I suppose I should have said that it was a British submarine but I thought my .uk address would be a bit of a giveaway....
The camera was definitely small, like the MX/ME series or OM's. It was not easily discernable against the bulk of the periscope, just looking like another of the electronic gizmo boxes that adorn those sort of things. Only when the periscope was turned did I spot the camera, in profile almost, and that was the last decent shot of it. Must see if the programme is repeated. My reasoning for suggesting the MX is that I thought that the most suitable candidate would be a totally manual camera. They will use a wide-latitude, fast film, so exposure is not critical. I don't know the OM series well at all but I think all of the shutters are electromechanical. Therefore, with that series and the ME types, you would (presumably) revert to an emergency setting once the batteries died. Thinking about it further, maybe an electromechanical shutter, with automatic exposure would make more sense. I'd better stop before I get confused..... mike