I HAVE experienced sitting on the bottom in a WWII era diesel boat. A boot camp comrade of mine was assigned to one of last diesel boats in USN, and I was invited to an open house which turned into a "visitors cruise" when the local ASW test and evaluation squadron requested a target for an evaluation exercise. After steaming surface and snorkel for about four hours, we dove deep and sat on the bottom of the Gulf of Mexico. Deep for that kind of boat was only 250 ft and our skipper (who had plenty of experience) made a nice soft landing in sand and we adopted about a ten degree list to port. Sweat, stink, mildew, and condensation everywhere, and the hull groaned on the way down. Enforced silence. Twenty minutes after liftoff the P-3 dropped a noisemaker on us. We could hear it hit the surface before it exploded. "Bang, you're dead!"
I later spoke with the techs working with the test equipment, and they said they could see us (in our North Atlantic color scheme) sitting on the white sandy bottom from 100 ft altitude.
Cheers,
Wes