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
Lambertsen Amphibious Respiratory Unit Émile Gagnan and Jacques-Yves Cousteau in 1943 and was not related to rebreathers; nowadays the word SCUBA is largely used to mean Gagnan's and Cousteau's invention and its derivatives.) Lambertsen designed the LARU while a medical student and demonstrated the LARU to the Office of Strategic Services (OSS) (after already being rejected by the U.S. Navy) in a pool at the Shoreham Hotel in Washington D.C. in 1942 The OSS "Operational Swimmer Group" was formed and Lambertsen's responsibilities included training and developing methods of combining self-contained diving and swimmer delivery including the LARU. Many diving rebreathers are descended from it.