As a young boy, Reynold Marion was fascinated with submarines. When he was 11 years old, he built a fully-submersible river raft made from 55-gallon drums! It worked - once.
Now, Reynold had made his dream a reality: he built a
boat/submarine hybrid submersible powerboat (called the Marion Hyper-Sub). This one's a prototype named The Fathom: Link | Video [YouTube] - Thanks Jon Jason!