With the first use of “poison gas” in World War I (The Battle of Ypres – 1915), it became clear that soldiers on the battlefield needed an immediate measure to counteract this weapon. Although designs for “Smoke Masks”, had been around for 15 years prior (and “Plague Masks” from The Middle Ages”) - nothing was effective for this new kind of warfare. The PH Hood (England), was a first attempt, (but failed to prevent certain types of gases or failed under saturation tests). This would lead to the “Hypo Helmet” (1915).
Made of canvas, the material was coated in Hypo Solution (Glycerin with Sodium Thiosulphate). This solution was somewhat effective at blocking Chlorine Gas. However, this device (while effective in the beginning) did not have a filtration system. Enter French designed M2 Gas Mask and The English Small Box Respirator. Both used a filter box (worn on the front). Made of canvas and leather, these would be the primary models used (and developed upon) – for later better made designs. Germany (the first Country to use poison gas in the War), was more prepared for individual protection of it's soldiers.
Form fitting leather masks (with build in filter canisters), were issued to all soldiers (on all Fronts). Even animals (used on all sides), were afforded protection from Gas. Horses and Mules were still used (pulling Supplies and of course in the “waning” Cavalry). Germany would retain it's primary design until the 1950s.