Abstract: An apparatus is provided for underwater operation comprising a pressure regulator configured to reduce a pressure of a gas received from a gas source at a first pressure to a second, lower pressure. A multiport differential pressure regulator is provided to receive the gas at the second pressure at a first port and to provide the gas to a second port at a differential pressure relative to an ambient pressure that varies based on a depth of the apparatus, where the differential pressure is set to a pressure that is at least 0.1 PSI below ambient pressure. A check valve vent is coupled to the second port of the multiport differential pressure regulator to relieve pressure at the second port accumulated by the apparatus during operation at a higher pressure depth when the apparatus rises from the higher pressure depth to a lower pressure depth.