Battle of Wuhan
Japan made heavy use of chemical weapons against China to make up for lack of numbers in combat and because China did not have any poison gas stockpiles of its own to retaliate. Japan used poison gas at Hankow in the Battle of Wuhan to break fierce Chinese resistance after conventional Japanese assaults were repelled by Chinese defenders. Rana Mitter writes, Japan also used poison gas against Chinese Muslim armies at the Battle of Wuyuan and Battle of West Suiyuan.