Ditto many of the comments above.
I get claustrophobic and didn't realize what the interior of the ride would be like. You file in and sit on long benches, one row back to back with the other row. Each person has a window in front of them, but there is not much room between your body and the window, plus you are squished next to the people around you. I, unfortunately, was right in the middle of our row - I wish I had known and asked to be at an end - maybe that would have helped a bit?
As others have said, I spent a good deal of the ride concentrating on breathing, assuring myself that the sub wasn't even underneath the water all the way, and with my face very close to the window to make it seem like there was more room. I also tried to take a lot of pictures (knowing they weren't turning out, but it kept my mind off other things) and watching a little girl who was thoroughly enjoying the whole ride.
All of those things helped, and I did make it through without screaming hysterically, lol, but not sure I would ever go on it again, even without the claustrophobia. I did think it was a cute ride, but certainly not worth a wait or to ride every visit - we all wanted to try it and see what it was about, so we did.