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
Diving regulator which gained widespread acceptance. This came about after French naval officer Jacques-Yves Cousteau and engineer Émile Gagnan met for the first time in Paris. Gagnan, employed at Air Liquide, had miniaturized and adapted a Rouquayrol-Denayrouze regulator used for gas generators following severe fuel restrictions due to the German occupation of France; Cousteau suggested it be adapted for diving, which in 1864 was its original purpose. The single hose regulator, with a mouth held demand valve supplied with intermediate pressure gas from the cylinder valve mounted first stage, was invented by Australian Ted Eldred in the early 1950s in response to