Fuel Cells

The attached ghost view of Ohio State's new fuel cell electric land speed car gives a good idea of the volume required by fuel cells sufficient to sustain 700 horsepower.

Since the car is intended for short sprints a large hydrogen tank is not required and oxygen (helox, actually) is carried in an internal tank instead of being drawn from ambient air.

Nevertheless, the car is a useful guide to those who have wondered about the feasiblity of applying fuel cells to watercraft such as a submersible.