Helen Dore Boylston was a young American nurse serving on the front lines of World War I, so she was no stranger to chaos. But the steady drone of hundreds of motors advancing towards her hospital in France in 1918 was unlike anything she had ever heard before. An air raid was underway and the shells came “so low that her hair stood on end with every screech,” she’d write later, but this sound was something else. 

When she looked to the horizon, she saw the source of the noise: illuminated only by the moonlight were an endless string of black ambulances, snaking as far as the eye could see. When the men they carried began arriving, their faces were ghost white and their wounds gaping and uncovered. Rows of them, blinded by their injuries, clung to each other to stay upright. Many of them, she noted, were mere teenagers.

It was going to be a long night but she wasn’t daunted. Boylston’s unit would go on to treat more casualties than any other group of American doctors and nurses. When the Great War ended later that year, claiming a staggering 40 million lives, Boylston—who had attained the rank of captain—was distraught.

“What are we all to do now? How can we go home to civilian life, to the never ending, never varying routine?” She wrote in her diary. “And the Twenty-second General Hospital, that vital living thing, saturated with the heights and depths of human emotion, will become a slowly fading memory of days when we really lived.”

Boylston was one of over nine million American women who joined the war effort. Not all of them faced the ravages of war firsthand––though many did, working as ambulance drivers who hurtled through artillery fire to rescue the wounded from the battlefield or to deliver emergency medical supplies to the front lines. Many women stayed home but worked in munitions factories or stitched surgical masks and gauze as Red Cross volunteers. Even librarians mobilized for war, building makeshift libraries in camps that would distribute nearly 10 million books and magazines to soldiers.

In total, the number of American women who joined the war effort dwarfed the nearly 5 million men who served in the armed forces.

Women’s sudden entrance en masse into both the war and public life brought a central injustice of American life into sharp relief: though they fought and died in the war, they could not vote for it. This irony helped to crystallize the battle for the vote that suffragists had been fighting for almost 70 years.