PHOTO RESEARCHERS, INC. / SCIENCE PHOTO LIBRARY PHOTO RESEARCHERS, INC. / SCIENCE PHOTO LIBRARY
Australian soldiers, wearing gas masks, in battle near the western front at Ypres, Belgium, during World War I. The first use of chemical warfare was on April 22 1915, when Germany released chlorine gas from cylinders at Ypres. The masks were simple respirators with a charcoal absorbent.
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