chemical warfare was used Chemical warfare using chloride gas was first released by German troops on April 22, 1915, killing 1,100 Allied soldiers and injuring an unknown number of others. An eyewitness account described the impact as "a burning sensation in the head, red-hot needles in the lungs, the throat seized as by a strangler." By the time the U.S. entered the war, gas masks such as this one had been developed with chemical absorbents that limited the impact of chloride gas