Aqua-Lung was the original English name of 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 ("lieutenant de vaisseau") Jacques Cousteau. It allowed Cousteau and Gagnan to film and explore more easily underwater.