In a French forest in late spring 1918, Elsie Janis, a 29-year-old American woman with short, curly hair and a wide smile, took a seat behind a 155-millimeter howitzer, ready to fire.

Janis, a singing, cartwheeling vaudeville star, had spent three months touring France, performing for the men of the American Expeditionary Force as they prepared to fight in World War I. A deep believer in the Allied war effort, she identified as a “doughgirl,” the tomboy pal or kid sister to tens of thousands of doughboys -- the popular term for America’s WWI troops. Long before the USO tours of future wars, her good cheer boosted morale. “Are we downhearted?” she’d shout. “NO!” the soldiers would shout back.

“Elsie Janis is as essential to the success of this Army as a charge of powder is essential in the success of a shell,” the Army newspaper Stars and Stripes declared. And one day around late May, just as Americans were joining the war’s combat en masse, Janis literally applied the powder’s charge.

Behind the howitzer, which was aimed at a German position, Janis grabbed the cannon’s cord and stood at attention. “Battery ready! Fire!” called an American general. Janis pulled the cord, then pulled again, and the gun fired. So did others around her. Soon, an observation post reported the German position destroyed.

“They told me I was the only woman who had fired regular hundred and fifty-five power hate into Germany,” she wrote in her war memoir The Big Show: My Six Months with the American Expeditionary Forces . The next day, her memoir recalls, she met an Army major from an artillery regiment that had named one of their two “Big Bertha” cannon after her, the other for Betsy Ross. “I am certainly proud,” she wrote, “for he says we were chosen as being American patriots.”

Though nearly unknown 100 years later, Janis was one of the war era’s most popular entertainers. A Columbus, Ohio, native, Janis had been a vaudeville performer since age 4, encouraged by her domineering mother, Jennie Cockrell Bierbower. On Christmas of 1899, at age 10, Janis performed at the White House for President William McKinley, even imitating the president, capturing his rigid posture, tight smile and deep voice. She debuted on Broadway at age 16 in the runaway hit The Vanderbilt Cup. She was a “consummate stage talent,” wrote historian David S. Shields for Still, a book about Broadway stars: “an impressionist of clairvoyant ability, a song lyricist who combined wit with sentiment, an actress of immense dynamism, a vibrant solo dancer, and a singer who could project to the gallery.”

For American soldiers, Janis was a reminder of women they knew back home. She projected a mix of conventional and audacious femininity, adventurous rather than maternal, spunky and blunt like the men she performed for. Wearing a white blouse, long pleated blue skirt, blue sweater and blue beret, Janis often invited soldiers onstage, not to dance with her, but to sing or dance solo. She performed “as a beloved kid sister, not as an unattainable sex object,” wrote historian Lee Alan Morrow in a 1998 essay.

Janis had regularly visited France and England with her mother since 1906, when she was 17. She was performing in The Passing Show, a musical revue in London, when the war broke out in August 1914. That fall, she started singing for British soldiers. She often sailed to England aboard the Lusitania , including a voyage in January 1915, four months before a German submarine sank the famed ocean liner. She rejected American neutrality in World War I long before America did. Her plaintive song protesting the Lusitania attack, “Where Are You, God?,” implored the almighty to stop Germany’s poison-gas attacks and bring peace.

In 1915, Janis’ star turn in The Passing Show set her opposite the dashing Basil Hallam, a British actor she’d met in New York in two years earlier. Their romance, which included talk of marriage, came to a tragic end in August 1916, when Hallam, serving in the British military, died during the Battle of the Somme, after his observation balloon broke loose from its cable and his parachute got caught in the balloon’s rigging.

“I was never really happy again until April 6, 1917,” Janis wrote – the day the United States entered World War I. “From that time on I had but one idea, and that was to get to France and do for our boys what I had done for the others.”

Janis and her mother financed her own tour of France in 1918, which she later called the “most glorious months of my life.” She performed on anything she could make into a stage: the backs of pickup trucks, shed roofs, airplane hangars. Morale-boosting entertainment for overseas soldiers grew as a phenomenon during World War I -- the YMCA deployed 1,400 volunteer entertainers to its camps in France, where soldiers took leave -- but Janis was the biggest American star to tour France in 1918.

Near the town of Minet-le-Tour, Janis performed in a boxing ring set down along the main road as church bells rang.

“The boys were in the trees, up poles, on fences,” she wrote. “As a finish I led the band and danced. When I turned my back on one bunch, which I could not avoid doing in the ring, they would moan and groan.” It reminded her of a revolving stage, “trying to face them all and only having one face!”

An expert mimic, Janis imitated stars of her day, including opera star Sarah Bernhardt, singing her war song “Joan of Arc,” and Will Rogers, complete with expert use of a lariat. Her earthy variety-show humor, filled with soldiers’ stories, patriotic songs, dancing and acrobatics, endeared her to the doughboys. She described one show in a French town in her 1932 autobiography, So Far, So Good! : “My performance consisted of telling stories filled with hells and damns, singing in a voice that was only mediocre, making the men sing with me, a refined little ditty entitled, ‘Oh, You Dirty Germans, We Wish the Same to You!,’ swinging legs that were -long but far from the French idea of comeliness, and finishing with cartwheels!”

Janis cheered the AEF on to war throughout spring and summer 1918. General John Pershing, the American commander in France named Janis an honorary general and gave her a Cadillac with an AEF Headquarters logo. A photo of Janis giving a military salute, her curls bouncing out from under the brim of a doughboy-standard steel Brody helmet, became famous.

In the summer of 1918, when thousands of American troops were killed and injured in the fights to stop Germany’s drive toward Paris, Janis spent three weeks in military hospitals, visiting and singing for wounded soldiers. “[I] tried to make them forget that they had wounds,” she wrote. “I could write pages of the bravery of our men… under real and terrible pain. Whether they had lost one leg or two, whether they would perhaps never see again, the smile was always there for me and my little jokes.”

Her shows during and after the war were filled with a gender-switching common in vaudeville: cross-dressing as a man, imitations of male stars, a dance with a prominent French lesbian actress, Eva Le Gallienne. Queer-studies texts have speculated about Janis’ sexual orientation, reading her marriage, at 42, to a man 16 years her junior as a possibly “bearded” arrangement. “Elsie attended parties at which same-sex desire was not masked,” Morrow wrote. At one, she arrived accompanied by the Broadway actress Marilyn Miller, while dressed in men’s clothes and carrying a riding crop.

In Janis’ public life story, at least, she cracked jokes about her many short romances with men, her fear of marriage, and her bachelorette-hood. “I don’t even keep my love letters,” she told a reporter – “I burned both of them.”

After the war, Janis spent years performing shows filled with patriotic war nostalgia. In the 1930s, after vaudeville faded, she worked as a screenwriter, memoirist, and a radio announcer. During World War II, she performed with Bob Hope for 4,000 troops in California and on Dinah Shore’s radio show, passing the torch of entertainer-supporting-the-troops to a new generation.

Janis’ most lasting romance was with her generation of American soldiers. Four hundred of them, middle-aged, many squeezed into their old uniforms, marched in her funeral procession in 1956. She once joked that her epitaph would be, “Here lies Elsie Janis, still sleeping alone.” Instead, her tombstone reads, “Sweetheart of the A.E.F.”