It was already a war crime to use chemical weapons when World War I began. Every major country had signed a convention agreeing not to use them. But when the fighting began, the treaties meant nothing.
Chemical warfare was an everyday horror of war. Men huddled in the trenches, watching for the creep of gas clouds or the telling smells that meant a toxic chemical was starting to choke their lungs.
The calls of “Gas! Gas!” that filled the air made World War I unlike any war that had come before it. It was a threat that there was a fate waiting for you that could be worse than death.