Scuba diving is swimming underwater while using self-contained breathing equipment.
By carrying a source of compressed air, the scuba diver is able to stay underwater longer than with the simple breath-holding techniques used in Snorkeling and Free-diving, and is not hindered by air-lines to a remote air source. The scuba diver typically swims underwater by using fins attached to the feet. However, some divers also move around with the assistance of a DPV (Diver Propulsion Vehicle), commonly referred to as a scooter, or by using surface-tethered devices called sleds, which are pulled by a boat.
The term SCUBA arose during World War II and originally referred to USA combat frogmen’s oxygen rebreathers, developed by Dr. Christian Lambertsen for underwater warfare. Today, scuba typically usually refers to the in-line open-circuit equipment, developed by Emile Gagnan and Jacques-Yves Cousteau, in which compressed gas (usually air) is inhaled from a tank and then exhaled into the water. However, rebreathers (both semi-closed circuit and closed circuit) are also self-contained systems (as opposed to surface-supplied systems) and are therefore classified as scuba.
Although the word ‘SCUBA’ is an acronym for “Self Contained Underwater Breathing Apparatus”, it has also become acceptable to refer to scuba as ‘scuba equipment’ or ‘scuba apparatus’.