During World War I, Germans experimented with numerous poisonous gases as weapons. After the first German chlorine gas attacks, Allied troops were supplied with masks of cotton pads that had been soaked in urine. It was believed that the ammonia in the pad neutralized the chlorine. These pads were held over the face until the soldiers could escape from the poisonous fumes. The Vickers machine gun, used by the British Army during World War I, required water for cooling when fired so soldiers would resort to urine if water was unavailable.