['< sod > * closed - circuit or semi - closed circuit scuba systems allow recycling of exhaled gases. this reduces the volume proportion of gas used, so that a smaller cylinder, or cylinders, than open circuit scuba equipment may be used for the equivalent dive duration, retaining and giving the ability not to spend far more time underwater compared to open circuit or for the same gas consumption. rebreathers also produce far less bubble volume and makes less noise than scuba, which makes them attractive to military, scientific and media corps divers. < ref name = " usn " / > < eod > < sod > * closed - circuit or semi - closed circuit [ [ rebreather diving | rebreather ] ] scuba systems allow recycling of exhaled gases. this reduces the volume of gas used compared with open circuit, so that a smaller cylinder, or cylinders, may be used for the equivalent dive duration. they provide the capacity to spend far more time underwater compared to open circuit for the same gas consumption. rebreathers also produce far possibly less bubble volume and less noise than scuba. this makes them attractive to covert military divers, who wish to avoid detection, scientific divers who do indeed not want to disturb the marine animals, and media divers who do not want their work obscured by bubbles. < ref name name = " usn " / > < eod >']