This month, Swedish scuba manufacturer Poseidon Diving Systems plans to introduce an electronically controlled closedâ¿¿circuit rebreather (CCR) called Discovery, which promises to change mainstream sport diving the way Microsoft Windows changed computing. Rebreathers, which have been around for decades, greatly increase dive time but at an enormous cost in complexity, training, and setup time. Poseidon’s new system is designed to do away with all that. In October, the company gave me the system for a 30-minute test splash during a trade show in Las Vegas.

To see what sets Discovery apart, let’s review some scuba basics. The conventional scuba equipment that Jacques Cousteau introduced in 1943 has an open circuit. The regulator supplies air from the tank, and your exhaled breath vents into the water as bubbles. Your body uses only a fraction of the oxygen in each breath; the rest is wasted. At higher pressures, each breath takes more from your cylinder, so you use up your air faster just when you need it the most—on your deepest dives.

A rebreather with a closed circuit gets around the problem by salvaging oxygen in your breath. You exhale into a counterlung, a gas bladder that expands and contracts as you breathe. The air then passes through a chemical-absorbent canister that removes carbon dioxide. Sensors analyze the oxygen content and direct the system to add either pure oxygen or regular air, whichever is needed to keep the oxygen concentration within its proper boundaries. The resulting gas goes to a second counterlung, then back to you when you inhale.

Closed-circuit rebreathers can give you seven times as much dive time as standard scuba equipment, regardless of depth. They also make it easier for your body to adapt to changes in water pressure, because they adjust the ratio of nitrogen to oxygen as you go up or down. The downside is complexity. It can take up to an hour, even for experienced divers, to set up and check a CCR compared with a few minutes for an open-circuit system. Then, underwater, CCR divers must decipher multiple readouts—including sensor readings, supply pressures, decompression status, oxygen exposure status, oxygen partial pressure, and scrubber life; recognize the combined effects of all those variables on dive time; and make what are in effect tens of thousands of implicit decisions. Even with electronic systems, problems aren’t always obvious.

So until now, sport use of CCRs has been limited to a relatively hard-core cadre of ”tec” divers who are willing to deal with these hassles and risks. Even many professionals have stayed with the simplicity of open-circuit scuba.

Discovery may change all that. It is the culmination of 20 years of design and development by Bill Stone, arguably the most innovative and experienced CCR engineer alive, famous for leading several milestone cave-diving projects.

Since the mid-1980s, Stone and other divers have used limited-production rebreathers that use computer controls to improve operation and make the device easier to use. He has taken his Cis-Lunar Mark III, IV, and V models, designed for science and exploration, to depths in excess of 120 meters—edgy stuff.