How were chemical attacks used in world war i? a. poison gas was sprayed over battlefields by airplanes to weaken enemy positions before major attacks. b. canister of position gas were launched into enemy positions so that clouds would kill or injure soldiers. c.mustard gas, while not deadly, was used to demoralize enemy troops prior to an attack. d. chemical attacks were used to clear barbed wire from no-man's-land so troops could advance.