The exact name of this repurposed MK.IV respirator (1939 dated) is unknown. It has a 1956 dated Nu Plac Products Chloropicrin filter attached. It is possible that this MK.IV respirator was repurposed by Nu Plac Products. After World War II military and civilian gas masks were sold / auctioned as surplus to companies and the public for the stripping of materials or repurposing etc.