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
Jacques Cousteau with the Cannes Film Festival 1951). Cousteau and the "Élie Monnier" then took part in the rescue of Professor Jacques Piccard's bathyscaphe, the FNRS-2, during the 1949 expedition to Dakar. Thanks to this rescue, the French Navy was able to reuse the sphere of the bathyscaphe to construct the FNRS-3. The adventures of this period are told in the two books "" (1953, by Cousteau and Dumas) and "Plongées sans câble" (1954, by Philippe Tailliez). In 1949, Cousteau left the French Navy. In 1950, he founded the French Oceanographic Campaigns (FOC), and leased a ship called "Calypso" from Thomas Loel