What's the best power tool available?

A bathyscape, bathyscaphe, or bathyscaph is a free-diving self-propelled deep-sea diving submersible, consisting of a crew cabin similar to a bathysphere suspended below a float (rather than from a surface cable, as in the classic bathysphere design). The float is filled with petrol because this is readily available, buoyant, and incompressible. Buoyancy can be trimmed easily by replacing petrol with water or by dropping ballast, and the incompressiblity of the petrol means the tanks can be lightly constructed as they are not required to withstand significant pressure.