Mike Donovon (Diver)
Preparing to leave on the Flying Sub, Nelson has Cara Sloan put on a flight jacket, explaining that it doubles as a life preserver if necessary. This is the only time that this innovation is mentioned. In "Killers of the Deep", seven episodes further on, they use standard life jackets.
As so often happens in cases like these, Dr. Sterling's clothing inexplicably grows right along with him. There is also no explanation for how the already sizeable Sterling got out of the habitat--or managed to avoid drowning!
Cara: You detest what you can't explain, don't you, Admiral?
Nelson: No, "detest" is the wrong word. I, I worry about things I can't explain, because those are the things that can hurt you.
In the book Science Fiction Television Series, Liam Sullivan recalled filming his giant underwater scenes in a 12-foot tank of water. After the third take, he was supposed to jump up, catch a wire stretched over the tank, and pull himself up. He missed the wire and fell back, completely out of breath. Two divers leaped in and pulled him up before he drowned. Three weeks later, Irwin Allen decided Sullivan's make-up wasn't scary enough, and they did it again. According to the Irwin Allen book, Sullivan insisted on having the tank half drained, so that he could get air more easily.