By Elizabeth Heideman
November 18, 2014

Now that the Pentagon has lifted the 1994 ban barring women from serving in special-operations and combat units, critics are waging a battle of their own, insisting that women lack the physical and psychological stamina that combat requires. While military officials insist they won’t soften their intense standards in order to allow more women entry, opponents argue that women will never be able to join otherwise, and that the Pentagon’s push for diversity will only result in a weakened United States military that places us at risk. Right now, the Marine Corps is in the middle of an experiment to test whether women can adequately perform the tough work required to defend the nation.

But American history is already full of women who can answer that question: during the Civil War, there were as many as 400 women who disguised themselves as men and fought for both the Union and the Confederacy. They pulled off their charades so well that few people today even know their stories.

“War actually shapes history, and history has always been about men,” says C.J. Longanecker, a historian and former ranger for the National Park Service. “But women were always there; they just didn’t get the press coverage.”

For one female soldier buried in Chalmette National Cemetery in Louisiana, it took more than 100 years to get the press coverage she deserved. Her story ends just east of New Orleans, where 15,000 headstones stretch out in seemingly infinite rows, interrupted only by the occasional oak tree.

Her story begins, though, in 1843 in Afton, N.Y., when a farmer’s wife gave birth to the first of her nine children—Sarah Rosetta, or just Rosetta. Like the lives of so many other women who enlisted as men, Rosetta’s life would revolve around hard labor and her family’s many debts. By the time Rosetta turned 19, she still had no marriage offers—a suffocating verdict for a woman who lacked both education and social status in the 19th century.

So Rosetta cut her hair, found a pair of men’s trousers and became 21-year-old Lyons Wakeman, leaving behind her family’s farm and fighting for independence in the only way that seemed possible.

She enlisted with the 153rd New York Infantry regiment, which encamped at both Alexandria, Va., and Washington D.C. before campaigning in Louisiana. In her book An Uncommon Soldier, Historian Lauren Cook Burgess has assembled Rosetta’s private letters to her family from the battlefield. As Burgess’ book shows us, Rosetta not only survived in a soldier’s life, she excelled at it:

“I don’t know how long before I shall have to go in the field of battle,” Rosetta writes. “For my part I don’t care. I don’t feel afraid to go…I am as independent as a hog on the ice.”

The eager young woman took to chewing tobacco and adopted all the “vices” that a typical soldier embraced. The five-ft.-tall Rosetta even won a brawl once with a much larger and much rowdier soldier than she, landing a few punches on him and no doubt earning some cheers from her comrades.

Rosetta eventually fought in another kind of battle, one more savage than she could have imagined. The Battle of Pleasant Hill took place in northwest Louisiana on Apr. 9, 1864. It was part of the Union Army’s push to capture the area from the Confederates. “There was a heavy cannonading [sic] all day and a sharp firing of infantry,” Rosetta writes. ”I had to face the enemy bullets with my regiment. I was under fire about four hours and laid on the field of battle all night.” Rosetta’s regiment launched a full frontal attack on the Confederates, with their commanding officers later praising the 153rd for their fierce bravery.

Meanwhile, the soldier seemed forever haunted by her oppressed past life as a farmer’s daughter. In letters to New York, Rosetta can’t help repeat that she will never return home, as if she had to convince not only her family, but also herself.

“If I ever get clear from the Army I will come home and make you a visit, but I shall not stay long,” Rosetta writes. “I shall never live in that neighborhood again.”

Had Rosetta lived, she may well have spent the rest of her days as a man, as multiple women actually did when the fighting was over. Rosetta, however, did not live. She fell prey to the menace that killed more than 413,000 soldiers in the Civil War—disease. After the Battle of Pleasant Hill, Rosetta and her comrades were forced to participate in a hellish two-day, 70-mile march through the untamed Louisiana wilderness, with many men collapsing from exhaustion and pain before reaching the end. Rosetta survived, but developed chronic dysentery.

By the time Rosetta’s ambulance reached the Marine U.S.A General Hospital near New Orleans 15 days later, she had deteriorated into the acute stages of her disease.

Rosetta languished for a month and then died. Lyons Wakeman’s cover, however, did not. In a stunning combination of luck and poor 19th-century healthcare, it seems the Army never discovered Lyons’ true identity. The military ironically lists Lyons Wakeman as an “honest” and “faithful” soldier, who died from chronic diarrhea while serving.

Back in New York, the U.S. census that took place shortly after the war makes no mention of a Rosetta Wakeman, only listing the now-dead Lyons. Rosetta’s family never mentioned their eldest daughter again, instead hesitantly referring to a long-gone sibling “who went by the name of Lyons,” according to Burgess’ research. It wasn’t until the 1970s, when Rosetta’s descendants examined a stack of faded letters kept in an attic, that the astounding legacy of Rosetta—aka Lyons—was made public.

Could the Army hospital have possibly never noticed Rosetta’s true gender? Experts say it’s more plausible than you’d think. “Even enlisting, they didn’t do a physical examination without any clothes on, and people didn’t look at other people’s naked bodies in those days,” says Longanecker.

Conspiracy theories, however, abound. Longanecker believes the nurses at Marine U.S.A. General sympathized with Rosetta’s desperate masquerade. “Because she had been in the Army for some time, and because she was a well-respected soldier, they didn’t say anything because it would have prevented her parents from receiving any compensation for her death,” Longanecker says. “It was a kind of hush-hush thing.”

While Rosetta’s death may still be clouded with unanswered questions, her military service and contribution to the war couldn’t be clearer. Today, as we raise the question of women’s readiness for combat, we only have to remember Rosetta Wakeman—and the countless other women who’ve secretly served alongside men—for our answer.

Contact us at editors@time.com.

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