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The Breath That Changed Everything
In 1943, French naval officer Jacques-Yves Cousteau and engineer Emile Gagnan tested a device they called the Aqualung in the Marne River near Paris. It was the first fully automatic demand-valve regulator — a system that delivered compressed air at ambient pressure, matching the diver's breathing rhythm exactly. Within a decade, it would transform scuba diving from a dangerous technical feat into a sport accessible to millions.
The Problem of Breathing Underwater
Early diving apparatus dated back centuries, but none solved the fundamental engineering problem elegantly. The hard-hat diving suit delivered constant-flow air through a surface hose — it worked, but at high depth the flow rate required became impractical and the diver was always tethered. Le Prieur's 1925 self-contained device used a manually-operated valve: the diver turned a wheel to release air, breathed it, and turned the wheel again. This was manageable for short dives but demanded constant attention and wasted enormous quantities of air.
The demand regulator concept — a valve that opens only when the diver inhales, delivering air at exactly ambient pressure — had been theorized but not successfully built for scuba application. The critical engineering problem was the balanced valve: in a demand system, the differential between the high-pressure tank and the ambient water pressure changes constantly as the diver ascends or descends. A poorly calibrated valve that delivers too much air causes hyperventilation; too little causes the diver to work against pressure to breathe.
Gagnan's Contribution
Emile Gagnan was a Parisian engineer employed by Air Liquide, the industrial gas company. In 1942, he had designed a demand valve for a specific wartime application: reducing-valve systems for city-gas injection into civilian cars, which France's petrol-starved population had begun running on compressed natural gas and wood gas. The valve controlled variable-pressure gas delivery — exactly the same functional problem as a diving regulator.
Cousteau heard of Gagnan's work through his father-in-law (who worked for Air Liquide) and approached him in the winter of 1942-43. Together they adapted Gagnan's valve for diving, routing the exhaust at mouth level to balance the inhalation resistance at depth — a key adjustment that earlier self-contained apparatus had not made. Cousteau tested a prototype in December 1942 in the Marne in freezing water. It didn't work perfectly: he could breathe standing up, but bending forward disrupted the balance.
Gagnan redesigned the exhaust-valve placement. The revised unit was tested in June 1943. It worked at every depth and in every body position.
The Patent and Commercial Production
Cousteau and Gagnan filed the patent jointly in July 1943. Air Liquide began manufacturing the device immediately for French navy combat swimmers. After the war, Cousteau negotiated the commercial rights for the United States with the Canadian branch of Air Liquide and founded a company called US Divers in 1949 to import and sell the Aqualung to the American market.
The price in 1952: $45 for the twin-cylinder backpack and regulator. Adjusted for inflation, this was significant but not prohibitive. Dive shops began selling them. Clubs formed. The sport began.
The Legacy
The Aqualung's core demand-regulator design has not fundamentally changed in 80 years. Modern regulators are smaller, more reliable, and significantly more sophisticated in their internal engineering, but the principle — a demand valve delivering air at ambient pressure — is identical to what Cousteau and Gagnan tested in the Marne on that June morning.
Every breath taken underwater through a modern regulator is a direct technological descendant of that device. Gagnan died in 1979. Cousteau died in 1997. The Aqualung outlived both of them.