A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is added to replenish the amount metabolised by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment. The purpose is to extend the breathing endurance of a limited gas supply, while also eliminating the bubbles otherwise produced by an open circuit system. The latter advantage over other systems is useful for covert military operations by frogmen, as well as for undisturbed observation of underwater wildlife. A rebreather is generally understood to be a portable apparatus carried by the user. The same technology on a vehicle or non-mobile installation is more likely to be referred to as a life-support system.
A fully closed circuit electronic rebreather (AP Diving Inspiration)
Oxygen rebreather KIP-8 interior showing the basic components
Russian firefighting rebreather KIP-8 exterior
Draeger Ray dive/surface valve with bite grip scuba mouthpiece, non-return valves, and breathing hoses
A frogman is someone who is trained in scuba diving or swimming underwater in a tactical capacity that includes military, and in some European countries, police work. Such personnel are also known by the more formal names of combat diver, combatant diver, or combat swimmer. The word frogman first arose in the stage name the "Fearless Frogman" of Paul Boyton in the 1870s and later was claimed by John Spence, an enlisted member of the U.S. Navy and member of the OSS Maritime Unit, to have been applied to him while he was training in a green waterproof suit.
A SEAL Delivery Team member climbs aboard a delivery vehicle before launching from the back of the submarine USS Philadelphia.
A 1945 British navy frogman with complete gear, including the Davis apparatus, a rebreather originally conceived in 1910 by Robert Davis as an emergency submarine escape set.
A French frogman with chest counterlung loop rebreather with two breathing tubes (model "Oxygers", 1957).
Royal Navy divers in Sladen suits during World War II