Many years ago I got this gas mask from an antique shop. I was pretty young and the guy who ran the place was nice so he just let me have it for free. From what I've researched it's probably from World War I and is either American or European. I was hoping someone here at r/askhistorians would have a more accurate discription of what I have. Thanks :)
It appears to be a British MK IV Service Respirator (2nd model). They were in production 1928–1939, but in use longer than that, in both the army (British and Commonwealth) and fire protection agencies. It can be distinguished from the 1st model MK IV by the way the fabric is stitched together and the number of holes on the nose cover.
See here (In German, unfortunately)