Australia's novel Old Children? Child scuba diving, Japan …….? submarine

Looking for an old book published in 1960 Australian or 1970. It was a children's story about a boy Australian who, when diving, there is a Japanese submarine sunk in WW2. Meanwhile, a Japanese man ill also is the submarine. The Japanese have air tank and lets the boy inside the submarine to die. A giant octopus kills the Japanese and the child is saved. I read as a child and now I want my child to read. If anyone knows the title or author of this book would be greatly appreciated. Thank you.

I have not been able to get to both. Can be one of the books by Percy Westerman, a prolific writer of adventure with some of his later works about the fall of the date of publication on the right, or perhaps one of the Willard Price books grip on your 'adventure' series, with Hal and Roger Hunt, remember that there were two or three that deal with various diving / Explodes under water, and definitely one with a giant squid / octopus put on a thrilling experience.

Children diving in Houston