The designer Waldemar Kops was part of the United Stated Chemical Warfare Service. He was a mask designer who "invented" several different types of gas mask face pieces during and after WWI. So, his masks would be seen from 1916 through the 1920s.

One of his most successful designs was used in the military for gas masks, and also in industry for several different types of protective masks, including the rebreather as shown here. Waldemar Kops most likely only designed the face part, and the rest of the rebreather is most likely an invention of MSA or another mining company. The same designer was part in the development of the RFK masks with a production a three million pieces! (RFK = Richardson, Flory and Kops)