while it looks like a large boat, the marion hyper-sub can dive completely under the water like a submarine. the boat is capable of high-speed travel on top of the water with a top speed of 75km an hour. under water the boat can dive to a depth of 250 feet allowing passengers to look up to the water’s surface above. the boat is in the prototype phase but has already made several successful test dives including one lasting 1 hour and 45 minutes using only the cabin air while under water. an 880hp engine drives the boat on the surface and under the water on dives.

http://www.hyper-sub.com