Colliam7:
Thread has evolved based on NJMike question. I really echo the no-penetration advice. You have to take your tank off and run a long hose through the hatch - very bad idea - or switch to a small pony, just to get into a very small, silt-filled space so you can say you did it. On the 352 you can even see the silt build-up through one of the open aft hatches.
Most divers, if they know what they are doing, can make it through the torpedo loading hatches. On the 352 this means the forward hatch as the aft hatch still has the at-sea supports blocking the way. I am 6'3" 250 lb and can get through in a dry suit with twin 100's. The key is to make sure that your chest is clean - no jacket BC's, not reels, or any other dangles. A small canister light is OK if you keep it tight.
Most divers can have a look (Head and one shoulder) through the forward battery access hatch (square hatch), the conning tower hatch, and after crews quarters hatch. But all of these hatches are tight, I could not get through with my tanks on.
The 352 is filled with sand and will not silt out very bad if you know what you are doing. The 85 and 853 (Block Island, RI) will silt out on you. I have been from the forward torpedo tubes all the way back to the engine controls (4 hatches back) on the 352. From the controls you can see the after torpedo loading hatch but the area between the engines has been sanded up and no one should go further then the controls.
The hatches on the 85 also have coral and other growth that can cut your suit up. The 701 is almost completly sanded in, so no penetration.
The Tarpon is only for the advanced wreck diver. The deck is at 140 and to penetrate the engine room you need to go down a 3' long hatch combing and will now be at 150 or so. You may very well need help getting out so someone has to be stationed at the hatch to help. The after torpedo hatch was blocked the last time I was on the wreck, but even if it is open, don't do it if you don't know what you are doing. The control room hatch is bigger and oval, and the forward torpedo hatch is also blocked.
Biggest thing to remember - DON'T DO IT IF YOU DON'T KNOW WHAT YOU ARE DOING.
Besides, subs are just sewer pipes with stuff in them. Have a look around for sharks and stuff on the outsides.