The invention is directed toward improved breathing comfort for an aviator subjected to rarified atmosphere at high altitudes. It employs a vest or jerkin which can be fitted by zipper over a passive pressure unit. The vest has secured to its interior a bladder which extends from front thigh up over the shoulder to the rear thigh position. A standard form of helmet is hermetically sealed to the neckline of the vest. Oxygen under pressure is introduced into the bladder and the helmet through a hand-operated valve which may be secured to the vest. This valve has three positions, (1) ''''Off,'''' (2) ''''Fill'''' and (3) ''''Mission Complete'''' and has a single tubing to the helmet and a double tubing to the bladder. One of the latter is employed for supplying the bladder with gas. The other of the double tubing contains a pressure-operated check valve which closes the passage between the helmet and the bladder in the event of bladder failure. The aviator would normally turn the valve, first to position (1) to supply the helmet with oxygen and to exhaust the interior of the bladder. He would then turn to position (2) which continues the oxygen supply to the helmet, and in addition, would fill the bladder with oxygen at a pressure as would make breathing more comfortable as the higher altitudes are reached. In the event that the bladder becomes punctured with flake or shrapnel and therefore unable to retain the gas, the valve is moved to position (3) to cause the oxygen, in excess of that necessary for the helmet, to escape to ambient atmosphere through the check valve.