Solo diving II. In the late 1940s, after the invention of the Aqua-lung by Cousteau and Gagnan, the first retail underwater breathing apparatus for sport was commercially marketed. As the sport expanded through the 1950s, several sporting organisations – notably the Young Men's Christian Association (YMCA) – began scuba training programmes for swimming enthusiasts, thus began the codification of what was believed to be proper practices for the expanding amateur sport of scuba diving. The buddy system was thought to be a useful corollary to the "never swim alone" edicts of the YMCA swimming and lifesaving programmes. Cousteau independently implemented a buddy
Scuba set regulator with high-pressure air tanks. This was patented in 1945. To sell his regulator in English-speaking countries Cousteau registered the Aqua-Lung trademark, which was first licensed to the U.S. Divers company, and in 1948 to Siebe Gorman of England, Siebe Gorman was allowed to sell in Commonwealth countries, but had difficulty in meeting the demand and the U.S. patent prevented others from making the product. The patent was circumvented by Ted Eldred of Melbourne, Australia, who developed the single-hose open-circuit scuba system, which separates the first stage and demand valve of the pressure regulator by a low-pressure hose, puts the