A bottom crawler is an underwater

Underwater

Underwater is a term describing the realm below the surface of water where the water exists in a natural feature such as an ocean, sea, lake, pond, or river. Three quarters of the planet Earth is covered by water...

 exploration and recovery vehicle. It is designed to sink to the bottom of a body of water, where it moves about using traction against the bottom with wheel

Wheel

A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

s or tread

Tread

The tread of a tire or track refers to the rubber on its circumference that makes contact with the road. As tires are used, the tread is worn off, limiting its effectiveness in providing traction. A worn tire tread can often be retreaded. The word tread is often used incorrectly to refer to the...

s. It is usually tethered to a surface ship by cables providing power, control, video, and lifting cababilities but this is not required.

Such devices have been proposed for use in recovering deep seabead minerals, such as manganese nodules.

These also have been considered since the late 1960s for use in offshore oil exploration

Oil exploration

Hydrocarbon exploration is the search by petroleum geologists and geophysicists for hydrocarbon deposits beneath the Earth's surface, such as oil and natural gas...

 and production in extremely deep water, but practical devices have used other technologies from the sea surface, such as moored barges and tension leg platforms.