KM-30M
Chinese helmet dated 1961 and marked "four-seasons wear," with the four point connection (five point, if you count the forehead hook) for the Russian KM-24 or KM-30 pressure-demand oxygen masks.
KM-30M mask in "ready" position.
The harness for the KM-30M is nightmarishly complex and mine arrived without instructions - this is my best guess as to how it goes together. Although the bladder is often presented as a "G" compensating device, I believe it was originally meant to automatically tighten the mask against the face while pressure breathing. Anyone who has suffered pressure breathing in an altitude chamber (or for real) can appreciate the utility of this approach. Clever design - the higher the pressure in the mask, the more the bladder is inflated, and the tighter the straps. The basic principle was kept with the KM-32 and subsequent masks, but the harness was simplified.
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