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
History of underwater diving develop the single-hose open-circuit scuba system, which separates the first and second stages by a low-pressure hose, and releases exhaled gas at the second stage. This avoided the Cousteau-Gagnan patent, which protected the twin-hose scuba regulator. In the process, Eldred also improved performance of the regulator. Eldred sold the first Porpoise Model CA single hose scuba early in 1952. In 1957, Eduard Admetlla i Lázaro used a version made by Nemrod to descend to a record depth of . Early scuba sets were usually provided with a plain harness of shoulder straps and waist belt. The waist belt buckles were