Gas mask carrier from the 60's/70's. This is the same style carrier that we have been using ever since except that with each successive issue of "webbing" the material that it's made of has changed along with some minor changes to the pouches and closure system(s). The carrier could either be worn on a purpose made shoulder sling or attached to the webbing belt. The flat pocket on the front is for holding chemical agent detector papers, decontamination mitts and nerve agent vapor detectors.
It is from the late 1950's, early 1960's and was the last version of Respirator Bag issued in conjunction with the 1951 Pattern Web. It has strong US influence in the design and as with most pieces of military equipment, these bags lasted in Canadian use well into the 1970s.