Brian, Early A-4s including the A4G used LOX [Liquid Oxygen] (Pure Oxygen Under Pressure). Dusty King demoed this story on the flight line after a first TA4G sortie. It was impressive. Some A4G pilots had a lingering cough worse than others (Ralph had a particularly bad response) especially to high G at low level. But as indicated a 'cough' usually fixed the problem. However after a long high altitude flight one could experience ear pain during and afterward as the excess oxygen leaked out of tissue to cause one to be constantly clearing one's ears (ou est ein buccaneer?). Youse could expect to wake at night at least once with ear pain to clear de ears. Anyhoo...
‘Where Are They Now? Paul Gillcrist’ by Barrett Tillman
Where Are They Now: Paul Gillcrist
Perils of Pure Oxygen Under Pressure
“...Another prominent influence in Paul's AirPac world was a female aviation physiologist at Alameda. He later learned that she was the first female aviation physiologist in the Navy. "A bunch of us were sitting in a briefing room awaiting the lecture on the use of oxygen equipment when this really attractive brunette walked in. We all sort of straightened up and paid attention. The young lady began the lecture by asking, 'How many of you smoke?' Several hands went up. Then, 'How many of you smoke while flying?' Some hands remained raised."
Without a further word, the physiologist strode to a console, inhaled deeply of 100 percent oxygen from a tank and produced a cigarette lighter. "This little gal blew a big breath, flicked the lighter and ignited a streak of flame right over our heads that seemed about six feet long," Paul recalls with a grin. Then she said, "That's why you don't smoke in the cockpit."
"Believe you me – she made her point! I thought, 'Hmmm... she's all right.'...”
There were sad stories of new USN A-4 pilots lighting up on cross countries to literally go down in flames (with cockpit filled with flames and smoke from the oxygen and any materials on fire).
Kiwis started with the LOX but then changed to a mixture of cabin air and oxygen (similar to Sea Venom system).