Somewhere around the turn of 1980s, a new improved version of the KM-34 was introduced. It's known as KM-34D. This new mask looks exactly as original KM-34 both on the outside and inside. After comparing both, KM-34 and KM-34D masks, I came to the conclusion that the difference most likely lies in the pressure valve. Original KM-34 masks were most likely using the pressure valve from KM-32 mask, so it seems logical that it either got replaced with some newer valve or the old valve was modernized. The change could be related to either to allow pilots fly higher, easier manufacturing of the valve itself or both at the same time. Another idea that worth noting here is that the change in designation could have been related to the introduction of the new oxygen system for new aircraft or ejection seats.   KM-34D shell from the front - it looks just like the older KM-34. Fiberglass shell has a KM-34D stamp. Inside, fiberglass shell is marked as KM-34D size 2 shell with 7148 ID number. Another tag inside of the fiberglass shell tells us that it was made in March 1981 - one of the first KM-34D masks produced. Rubber mask has it's own stamp which gives us its name, size and year of production. Inside KM-34D mask looks excatly like KM-34 mask. Shown here is the late production model of the KM-34D mask with a built in microphone. External microphone wiring. Mask's microphone plug. Microphone placement inside of the mask's rubber insert. Markings on the microphone bump of the rubber insert. ID sticker on the mask's hard shell. Date of production sticker located inside of the hard shell. Couple of shots of the late production KM-34D mask and ZSh-5 helmet...