Aqua-Lung was the first open-circuit, self-contained underwater breathing apparatus (or "SCUBA") to reach worldwide popularity and commercial success.

This class of equipment is now commonly referred to as a diving regulator or demand valve.

The Aqua-Lung was invented in Paris during the winter of 1942–1943 by two Frenchmen: the engineer Émile Gagnan and Naval Lieutenant Jacques Cousteau. It allowed Cousteau and Gagnan to film and explore more easily underwater.

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