What Do Navy SEALs Use to Breathe Underwater? Rebreathers vs. Open-Circuit Scuba
The short answer
Military combat divers generally breathe from closed-circuit rebreathers rather than the open-circuit scuba you rent at a dive shop. A rebreather recycles exhaled gas: it scrubs carbon dioxide out of the loop, adds oxygen back in, and sends the same gas around again, so little or nothing escapes as bubbles. Open-circuit scuba does the opposite — every breath you exhale leaves the system and rises to the surface. Specific hardware used by specific military units is not something the public record reliably describes, so this page sticks to the equipment categories and how they are specified.
Open circuit: the gear most divers learn on
An open-circuit set is a cylinder of compressed gas, a first-stage regulator that drops tank pressure down to something close to ambient, and a second stage you breathe from. You inhale fresh gas, you exhale it into the water. It is simple, rugged, cheap to service, and easy to teach, which is why recreational training is built around it.
Its weakness is gas duration. Because a regulator delivers gas at ambient pressure, each lungful at depth contains far more molecules than the same lungful at the surface. Deeper dives drain a cylinder faster, and that constraint is one of the reasons recreational planning tables and the depth ceilings that go with them exist at all — see why recreational diving stops at 130 feet.
Closed circuit: how a rebreather is different
A closed-circuit rebreather routes exhaled gas through a flexible counterlung and a canister of carbon dioxide absorbent, then back to the mouthpiece. Oxygen is what the body actually consumes, so the only gas that has to be replaced is the oxygen metabolized, plus whatever is needed to keep the loop full as volume changes with depth.
That produces three practical differences:
- Endurance does not collapse with depth. Oxygen consumption tracks how hard the diver is working, not how deep the diver is.
- Almost no bubbles. That matters for stealth, for noise, and for approaching skittish marine life.
- Warm, humid gas. Recycled gas has already been breathed, so it is less drying and less chilling than dry compressed gas from a cylinder.
Mixed-gas closed-circuit units add an inert diluent gas and control the oxygen fraction electronically. Pure-oxygen closed-circuit units carry no inert gas at all, which means no nitrogen loading to track — but oxygen partial pressure climbs with depth, which is why oxygen loops are specified for shallow work only. The same arithmetic governs enriched air in recreational diving; see nitrox maximum operating depth for how that calculation is actually run.
Why recreational divers mostly do not use rebreathers
Cost is the obvious one: a complete unit, plus absorbent, plus oxygen sensors that get replaced on a schedule, is a different order of expense from a regulator and a tank. Beyond money, rebreathers demand a long pre-dive assembly and checklist routine, periodic sensor calibration, and far more maintenance discipline. Training is a separate specialty track layered on top of open-water certification rather than part of the standard entry course content published by the recreational standards council, WRSTC.
Where the rules for professional divers live
If you are curious about the professional side rather than the military side, the written standards are public. In the United States, working-diver operations fall under OSHA's commercial diving standard, 29 CFR Part 1910 Subpart T, which addresses equipment, team composition, and procedures by mode of diving. Federal scientific divers work under the NOAA Diving Standards and Safety Manual, and university and research programs commonly follow the AAUS standards for scientific diving. None of those are recreational credentials, and none of them substitute for each other — the distinction is spelled out in recreational certification vs. commercial diving credentials.
The takeaway
The reason military divers use rebreathers is not that rebreathers are a better version of scuba. They are a different trade: more complexity, more cost, and more procedure in exchange for bubble-free operation and depth-independent gas duration. For a recreational diver taking a two-tank boat trip, open circuit wins on every axis that matters.