Actually now that I am looking at that picture closer, is that really a submarine? Or is it a torpedo that they have put a windshield and seats in and strapped a couple poor scuba divers into?
Don’t knock it. Its a swimmer deliver vehicle. SEAL’s use them, too, but ours are better. http://en.wikipedia.org/wiki/Advanced_SEAL_Delivery_System
Something - a tanker, a freighter, a sub, carries near a target and the swimmer deliver goes the rest of way. Its pretty big, so it may have a long range, or a big payload. It would be kinda ugly if a frogman delivered a big limpet mine, to, say, a LNG carrier. Oil terminals in the Gulf could also be good targets.