The Swiss FEGA C-Maske was the civilian version of the Swiss GM-33. Unlike its predecessor, it was made of smooth green rubber, and the filter was attached directly to the mask. This example was made by Feuerschutz Gasschutz around 1938.
Maske = "Mask"
Feuerschutz Gasschutz = "Fire Protection Gas Protection"
Similar masks in my collection: Swiss GM33