Scuba diving generates millions of dollars in revenue each year. The word “scuba” is an acronym for “self-contained underwater breathing apparatus,” created by the U.S. Navy as a way to describe the equipment used by military divers. It is fitting that the modern name for the popular underwater breathing equipment finds its origins with the military. For centuries before scuba gear was used for recreation or research, the ability to remain underwater for long periods of time was most desired for military purposes. Renaissance strategists fantasized about the ability to work on the underside of submerged vessels for long periods of time or, more importantly, being able to ambush enemies completely undetected.

Some early inventors, like 16th century Italian mathematician Niccolo Tartaglia, envisioned a waterproof bell or hourglass inside which a person could stay underwater for as long as the air encased remained breathable. Others envisioned air tubes that connected the diver to the surface. Even Leonardo da Vinci had a working model: in the 15th century, he sketched a diving suit that afforded the wearer the ability to descend or ascend by deflating or inflating a “wine skin to be used to contain the breath.” While many of these inventions never made it past the drawing board, they are quite impressive considering the lack of dependable scientific knowledge at the time.

A commercially viable diving suit was not produced until the 19th century. French engineers Benoit Rouquayrol and Auguste Denayrouze teamed up to produce the “Aerophore,” a suit that incorporated a reservoir of compressed air for emergencies. The reservoir gave the diver freedom to move around, for a small amount of time, unfettered underwater. The success of Rouqauyrol and Denayrouze’s compressed air reservoir inspired others to try and improve on the design. In 1878, Henry Fleuss designed the first self-contained oxygen apparatus. In his invention, oxygen was contained in a small copper cylinder that could be rebreathed, as the system used a chemical to absorb exhaled carbon dioxide. Furthermore, Fleuss’ apparatus did not produce air bubbles, making it ideal for military frogmen, as they would not be given away at the surface while using it.

As technology advanced, cylinders that could hold very high pressures were finally produced. This innovation, along with an observation made by French navy Commandant Yves Le Prieur, combined to create the first incarnation of modern scuba diving equipment.

In 1912, Le Prieur watched as Maurice Fernez remained underwater through the aid of a surface pump. Inspired by Fernez’s display, Le Prieur wanted to find a way to do the same thing underwater. Fourteen years later, the two men teamed up and produced the lightweight breathing apparatus that Jacques Cousteau would later refine and popularize. By attaching a mouthpiece to the kind of metal cylinder used to inflate pneumatic tires, Le Prieur was able to create a selfcontained breathing apparatus that was light and easy to use. However, the air flowed continuously out of the cylinders, giving the diver a mere 12 minutes underwater.

In 1943, Jacques Cousteau and Emile Gagan co-invented the first open-circuit scuba diving equipment, which they called the “aqualung.” It solved the problem of continuous airflow with the “demand valve,” which releases air only upon inhalation. Their invention was soon in widespread use. Cousteau is credited with popularizing modern diving and pioneering underwater filming, neither of which would have been possible without his invention. Though modern scuba diving equipment is fairly similar to the aqualung, it has undergone some changes. One of the most notable is Ted Eldred’s invention of a single-hose open-circuit scuba set, as opposed to the twin-hose design of Cousteau and Gagan. Scientists, vacationers, and militaries now use scuba equipment, assisting divers in a much broader range of functions than those originally conceived by Renaissance thinkers.