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
Aqua-Lung and adapted it to gas generators in response to a fuel shortage, which was a consequence of German requisitioning. Gagnan's boss, Henri Melchior, knew that his son-in-law Jacques-Yves Cousteau was looking for an automatic demand regulator to increase the useful period of the underwater breathing apparatus invented by Commander Yves le Prieur, so he introduced Cousteau to Gagnan in December 1942. On Cousteau's initiative, the Gagnan's regulator was adapted to diving, and the new Cousteau-Gagnan patent was registered some weeks later in 1943. After the war, in 1946, both men founded La Spirotechnique (as a division of Air Liquide) in