Most people are familiar with the immense amount of human casualties during World War I, though what is often overlooked is the large number of animals who perished during the war. More than eight million mules, horses, and donkeys on both sides died. Just like human soldiers, mules needed protection from the toxic gasses used on the frontlines of battle, so special gas masks were developed just for them. Sadly, not all animals were given gas masks, causing the hospitalization of thousands of animals (primarily horses). Aside from mules, horses, and donkeys, animals such as dogs and pigeons played a major role in the war effort on both sides.