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/La Spirotechnique coined by Cousteau himself on that purpose. In the USA during World War II the American military physician Christian J. Lambertsen designed a wartime frogman's rebreather which in 1952 got called the SCUBA (acronym for Self-Contained Underwater Breathing Apparatus), and later the name (changing to 'scuba' and treated as a word) was used to mean any underwater breathing set. In Britain the word "aqualung" became a generic trademark for open-circuit underwater breathing sets and stayed so for many years. The word "scuba" became the generic word quickly in the USA and eventually in Britain. For more information see Aqua-lung#Trademark issues.