Cousteau experimented with various underwater breathing devices, but found them cumbersome and ineffective. He envisioned a self-contained underwater breathing apparatus (SCUBA) that would allow divers to move freely and remain submerged for extended periods.

Cousteau partnered with Émile Gagnan, an engineer at Air Liquide, to develop the Aqua-Lung. Gagnan adapted a pressure regulator used for gas engines to deliver air to divers at the correct pressure.

Cousteau and Gagnan successfully tested the first Aqua-Lung in the Marne River near Paris. This breakthrough allowed divers to breathe underwater for the first time without being tethered to the surface.

After World War II, Cousteau and Gagnan refined the Aqua-Lung design and began to commercialize it through their company, La Spirotechnique. The Aqua-Lung quickly became popular among divers worldwide, revolutionizing underwater exploration.