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.
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Good design just works
Scuba
Scuba diving is a mode of underwater diving in which the scuba diver uses a self-contained underwater breathing apparatus (scuba) which is completely independent of surface supply, to breathe underwater.