This was one of my favorite model ship movies growing up. It was one of the first movies on which L.B. Abbott supervised the special photographic effects after being made the head of the 20th Century Fox special effects department in 1957. Surprisingly the film does not even get a mention in his very good book covering his career “Special Effects – Wire tape and Rubber band style” published by the American Society of Cinematographers.
The miniature effects are textbook in execution. There is a level of opacity to the underwater shots though possibly still a shade more transparent than you would get with a real submarine underwater. The miniature pyrotechnics are spectacularly effective. You can already see a particular L.B. Abbot style in the photography which matches his subsequent work ranging from Tora Tora Tora to Batman the movie.