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
Scuba set of 1918), and Commandant le Prieur's hand-controlled regulator in France (as of 1926); see Timeline of diving technology. This system consists of one or more diving cylinders containing breathing gas at high pressure, typically , connected to a diving regulator. The demand regulator supplies the diver with as much gas as needed at the ambient pressure. This type of breathing set is sometimes called an "aqualung". The word "Aqua-Lung", which first appeared in the Cousteau-Gagnan patent, is a trademark, currently owned by Aqua Lung/La Spirotechnique. This is the first type of diving demand valve to come into general use, and