Aqualung is the title of an album and a hit song by the rock band Jethro Tull, who had not at the time realised that the word was a trademark.

Aqua-lung was the original name for the first open-circuit SCUBA diving equipment, developed by Emile Gagnan and Jacques Cousteau in 1942. It consists of a high pressure diving cylinder and a diving regulator that supplies the diver with breathing gas at ambient pressure, via a demand valve. Before that, there were a few attempts at constant-flow compressed-air breathing sets.

In Britain, for very many years after public interest in scuba diving began around 1953, the word "aqualung" was commonly used in speech and in publications as a generic term for divers' open-circuit demand-valve-controlled breathing apparatus; and also in figurative uses such as "the water spider's aqualung of air bubbles". The word got into the Russian language as a generic noun "akvalang".

Over time, "SCUBA" came into common usage for that type of equipment, but with the increasing popularity of a different, "closed circuit" type of SCUBA, named the "rebreather", a need has arisen for another short but precise word to describe the original open-circuit SCUBA.

See also

• Timeline of underwater technology for details of this development.
• Scuba sets for description of modern breathing sets.
• Aqua Lung manufacturers site (English, French, German, Italian, Chech, and Japanese language versions available)

Aqualung and Aqua Lung are registered trademarks for diving equipment.