Plot: 17 year old Don Miller has been helping his uncle with a new Atomic Sub that can go lower in the sea than any before, and the military is interested. They come in and take over, but, luckily for Don, the guy taking his place is sympathetic, so he 'gets sick' and forces Don to take his place. After an encounter with an amorous whale, the crew gets captured by Atlanteans, who are apparently Cro-Magnon men that stumbled upon a way to generate amazing force fields and live on the ocean floor in a bubble city.
The crystals they use to power said force fields, however, are scarce, and they're running out. Their technology, while advanced in some ways, was mostly 'trial and error' engineering rather than research and theory, so they had no replacement. Don, of course, being a smart red-blooded American lad of the 50s, figures it out right away, and convinces the Atlanteans to go to the surface and get help, while sharing their force fields to prevent nuclear holocaust. The end!
Analysis: Modern 'Young Adult' writers sure could take some lessons from Lester Del Rey! This is almost the perfect YA novel (not sure if that was the intent).. the only thing that's missing is a bit of romance (women are nearly complete absent). it's a fun, fast moving story, with a couple twists( like Don's Dog being worshipped as a god, and an old salt named Muggins living with the Atlanteans), and a happy ending. Don is a complete Marty Stu character, and that's just fine, he's supposed to be. Del Rey has some points to make, from the down side of isolationism to the value of theoretical science vs. engineering, and makes them well without bludgeoning you with them.
I think it's meant to be timeless (the Russians are mentioned by name) but it's still a bit dated.. one of the crew is referred to as 'the Negro', and there's a two page 'please don't investigate me McCarthy' explanation on how the Atlanteans aren't actually a socialist society, even if they kinda are.
Those just add to the charm, though... definitely a great read!