The Siebe Gorman Salvus is a light oxygen rebreather for industrial use or in shallow diving. Its duration on a filling is 30 to 40 minutes. It was very common in Britain during World War II and for a long time afterwards. Underwater the Salvus is very compact and can be used where a diver with a bigger breathing set cannot get in, such as inside cockpits of ditched aircraft. It was made by Siebe Gorman & Company, LTD in London, England. It was designed in the early 1900s.

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.