German gas mask for horse, 1914-1918. Horses were used extensively during the First World War, being called on to perform tasks such as pulling ambulances full of wounded men or moving heavy artillery pieces. Gas warfare was first used by the German Army in 1915, although quite soon after both sides were using it. Protective equipment was slowly developed for both men and horses. This gas mask was designed to fit over the horse's nose. The Germans actually developed several types of gas masks for horses, and even one for dogs. This gas mask was found at a German equipment dump in France in August 1918 by the British Army.