The tale began in 1977 at the US National Oceanic and Atmospheric Administration (NOAA), where diving programme head Dr J. Morgan Wells came up with the notion that, instead of air, NOAA scientists should start using a diving gas containing less nitrogen and more oxygen. This would enable them to carry out longer dives with no required decompression stops or planned decompression dives with less hang time than air dives with the same profile.

It took a while for sport divers to start using rebreathers, although if you look back far enough, you can see that people were using them to go underwater for sport well before the Aqua-Lung came along. In his excellent book, The Darkness Beckons, Martyn Farr wrote that UK amateur cavers were using ex-government/military oxygen rebreathers in 1945. Farr also reported that the first sport diving rebreather fatality took place on a British sump dive in 1949.

Submarine rescue and recovery was the incentive behind the series of deep-diving trials conducted by the British Admiralty during the ‘30s, ‘40s and ‘50s. Setting out to extend the deep-diving limits, the Royal Navy programme established a world depth record in 1948, of 540ft. Wearing a Siebe-Gorman six-bolt helmet incorporating the Davis Injector system, flexible dress, and using the fast-dwindling supplies of American Lend-Lease helium, Petty Officer Wilfred Bollard set a depth record that was to last eight years. Not until 1956 would the baton pass to another.