The GM-38 was used by the German Army in World War II (the one in the picture was issued in 1938) and was created as an upgrade for the GM-30. It was produced by the manufacturing companies; Drager and Auer. The mask's face piece was made entirely from rubber, which supposedly protected against newly discovered chemicals.
This mask has a variety of colours, which represent why they were used. The mask on the right was used in the tropics of Africa in World War II as it is painted in 'sand colours'. The mask has a 5-pointed strap harness which is tightened with two straps in the mid-section and another two near the bottom. The mask was issued in a canister which was carried around the neck but the mask also has its own carrying strap with which it could be carried. The mask's filter thread is 40mm and the filter is quite heavy and the frontal weight pulls the mask forward.
After world war 2, some gas masks were in limited use with Austria.
The GM-38 series was very advanced for its time, with some models incorporating voice emitters and microphones.
A special variant of this mask was used by pilots. It had a hose on the left/right (depending on the aircraft it was used in).
For more information/display of this mask check out the following video: