With the doughboy (M1917) helmet and the gas mask.

Poison gas killed an estimated 91,000 people during World War I, so there was plenty of reason to fear and train for it in World War II. Despite the rare humorous poster below, this was no laughing matter.

In 1925, the League of Nations adopted the Geneva Protocol, which banned the use of chemical or biological agents in warfare--but it did not prohibit further development or stockpiling of them. During World War II, the battlefield prohibition mostly held--but there were the Nazi concentration camps.

During a basic training exercise in 1970, I had to walk around a room full of tear gas, then remove my mask some time before being let out. This was to show that masks worked, and that gas worked if you weren't wearing one. But the war we were pointing toward featured napalm and Agent Orange, for which gas masks provided poor protection.