I found yr comments interesting, I would have thought that the weakest point of the pressure hull would be anywhere a moveable protrusion needed to exit the pressure hull..i.e the propellor shafts the Hydroplane shafts ..I must admit the torpedo hatch would certainly have some degree of weakness to adverse pressure as it must provide a sealable yet semi-rotable access to the pressure hull...when u say crush depth...is that defined as the point of pressure hull metal collapse ? Please advise as to the nature of the seals around the propellor shafts of the diesel boats am most interested to know how they were constructed . regards Tom