It was a recreational submarine - not a military one nor a Disneyland ride. This was on Grand Cayman Island. It was a real submarine and you can see by the depth gauge that we actually submerged. Once down there, we puttered around the reef and watched fish, some scuba divers, and a large turtle swim by. Everyone had a window seat. I am a bit claustrophic and the thought of being underwater in a tube made me very nervous, but I did it, eventually I relaxed and enjoyed it.
Steve served onboard submarines in the US Navy and I had an opportunity to tour his sub when it came out of the yard and before it sailed for parts unknown. Even though it never submerged while I was aboard, I was still bothered by claustrophobia in the tight confines. His tours of duty lasted 3 months underwater without seeing dry land - well, actually without seeing anything but the inside of the sub. He did four tours while I waited onshore in Groton, Connecticut. He rated the recreational sub as little more than an amusement park ride, but it was enough for me to check it off my list.