Buddy diving just before and after the Second World War. After the invention of the "aqualung" by Cousteau and Gagnan, the first commercially underwater breathing apparatus became available for sale for sporting purposes in the late 1940s. As the new sport of scuba diving rapidly expanded through the 1950s, several sporting organisations—notably the YMCA—began programmes to train swimming enthusiasts in this new aquatic pastime, and began to codify what they believed were proper practises for this expanding sport. The YMCA considered the buddy system a useful corollary to the "never swim alone" rule of their swimming and lifesaving programmes. Cousteau himself independently
History of underwater diving regulator was adapted to diving, and the new Cousteau-Gagnan patent was registered some weeks later in 1943. Air Liquide started selling the Cousteau-Gagnan regulator commercially as of 1946 under the name of "scaphandre Cousteau-Gagnan" or CG45 ("C" for Cousteau, "G" for Gagnan and 45 for the 1945 patent). The same year Air Liquide created a division called "La Spirotechnique", to develop and sell regulators and other diving equipment. To sell his regulator in English-speaking countries Cousteau registered the Aqua-Lung trademark, which was first licensed to the U.S. Divers company (the American division of Air Liquide) and later sold with La