Types of Scuba Diving

Scuba diving is a mode of underwater diving in which a scuba diver uses a self-contained underwater breathing apparatus (scuba) to breathe underwater. Unlike other modes of diving, which rely either on breath-hold or on breathing gas 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 airline or diver's umbilical and longer underwater endurance than breath-hold.
Types of Scuba Diving
Rebreathers
The closed-circuit rebreathes were first developed for military use, due to their stealth advantages. The first commercially successful closed-circuit scuba was designed and built by English diving engineer, Henry Fleuss in 1878, while working for Siebe Gorman in London. His SCBA (self-contained breathing apparatus) consisted of a rubber mask connected to a breathing bag, with (estimated) 50-60% O2 supplied from a copper tank and CO2 scrubbed by rope yarn soaked in a solution of caustic potash; the system giving a duration of about three hours.
Sir Robert Davis, head of Siebe Gorman, perfected the oxygen rebreathe in 1910 with his invention of the Davis Submerged Escape Apparatus, the first practical rebreather to be made in quantity.
Rebreathers have been increasingly used by civilians for recreation, especially since the end of the Cold War. This reduced the perceived risk of attack by Communist Bloc forces, including by their combat divers. After that, the world's armed forces had less reason to requisition civilian rebreather patents, and automatic and semi-automatic recreational diving rebreathes started to appear.
Open-circuit scuba
The first commercially successful scuba sets were the Aqualung twin hose open-circuit units developed by Emile Gagnan and Jacques-Yves Cousteau in 1943, in which compressed air carried in back mounted cylinders is inhaled through a demand regulator and then exhaled into the water adjacent to the tank.
The single hose two stage scuba regulators trace their origins to Australia, where Ted Eldred developed the first example of this type of regulator, known as Porpoise scuba gear. This was developed because patents protected the Aqualung's twin hose design. The single hose regulator separates the demand valve from the cylinder, giving the diver air at the ambient pressure at the mouth, rather than ambient pressure at the top of the cylinder.