His superior had instructed him to cooperate with undersea explorer, Jacques Cousteau in any way, as his father-in-law was on the Board of Directors. Cousteau had been looking for a way to allow divers to remain underwater for several hours. Gagnan had just put together a regulator that would allow the use of cooking gas in an automobile. Gagnan and Cousteau decided that the cooking gas regulator was probably a better idea than the high-altitude breathing regulator. So with minor adaptations, this regulator became what Cousteau coined as "Aqua-Lung," the beginning of the modern-day SCUBA (Self Contained Underwater Breathing Apparatus).
In 1943, Emile and Cousteau perfected the Aqua Lung and Cousteau and his team of divers began underwater testing in the Mediterranean Sea. A century-old dream became reality - the first automatic autonomous diving suit, equipped with pressure regulator and compressed air bottles, gave the diver complete independence of movement.
The Aqua-Lung used cylinders of compressed air and was equipped with a demand regulator, which adjusted the air pressure automatically, and supplying air as the diver needed it. With some variations and some major improvements the Cousteau-Gagnan Aqua-Lung open-circuit system is still universally used today.
Its simple design and solid construction provided a reliable and low-cost unit for sport diving. The device revolutionized man’s perception of the planet. Not unlike the Portuguese, Spanish, and Chinese explorers of the fifteenth century who doubled their knowledge of the size of the world, Cousteau and Gagnan helped open a vast portion of the globe to human exploration. They offered the opportunity for extensive undersea investigation to enthusiastic scientists, engineers, and sportsmen.
In 1946, the first production models of the Aqua Lung were manufactured and sold in France. A year later, Emile and his family immigrated to Montreal, Canada, where he set up his workshop and later introduced the Aqua Lung to the United States. He continued his research and developed further inventions that have helped make scuba diving what it is today.