Here is a excellent book about this.
https://www.amazon.com/Shadow-Divers-Adventure-Americans-Everything/dp/0739320831#:\~:text=The%20%E2%80%9Cshadow%20divers%E2%80%9D%20of%20the%20title%20are%20deep,much%20beyond%20when%20Jacques%20Cousteau%20helped%20invent%20it.
Try Shadow Divers... I think he might like it! https://www.amazon.com/Shadow-Divers-Adventure-Americans-Everything/dp/0739320831