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
Aqua-Lung than its precursor, which in fact was almost completely unknown outside France. In addition, and most importantly, the Aqua-Lung could be mounted on stronger and reliable air tanks holding up to 200 atmospheres, allowing extension of diving duration to more than an hour at significant depths (including the needed time for decompression stops). The first Cousteau-Gagnan Aqua-Lungs (like the CG45 of 1945 or the Mistral of 1955) were mainly twin-hose open-circuit scuba. They have since been made by various manufacturers with varying design details and numbers of cylinders. Like modern open-circuit scuba with single-hose regulators, they consisted of one or