Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater.
Unlike earlier diving, which relied either on breath-hold or on air pumped from the surface, scuba divers carry their own source of breathing gas, (usually compressed air), allowing them greater freedom of movement than with an air line. Both surface supplied and scuba diving allow divers to stay underwater significantly longer than with breath-holding techniques as used in free-diving.
A scuba diver usually moves around underwater by using swimfins attached to the feet, but external propulsion can be provided by a diver propulsion vehicle, or a sled pulled from the surface.
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