In honor of Women’s History Month, we’d like to highlight barrier-breaking women in U.S. Military history. The list of women who have broken through discrimination and other barriers to full military service is long, but we’ve selected a few standouts.

Harriet Tubman, US Army

Harriet Tubman escaped the human bondage she was born into and spent a good portion of her life as a freedom fighter helping others escape the horrors of slavery. When the Civil War began, she realized that joining forces with the Union Army would make her efforts more effective. She first served as a battlefield nurse, and later became a spy who led a team of 10 men with the direct blessing of the U.S. Secretary of War. She became the secret weapon of the Union Army and was even referred to in some circles as “General Tubman.” Her personal contributions to the Civil War were significant and instrumental in helping the Union succeed.

Despite her heroism during the war, she was not recognized for her service or awarded the pension afforded to soldiers or nurses. Many people petitioned on her behalf, including some members of Congress. In 1899, some 34 years after the war ended, the House and Senate enacted legislation granting Harriet Tubman a pension of $20 a month, close to the amount given to other Civil War Veteran soldiers.

Through her incredible bravery and commitment during the Civil War, Tubman briefly forced open a door that would remain closed to women of any color for many decades to come.

Loretta Perfectus Walsh, US Naval Reserve

Ms. Walsh holds the distinction of being the first woman to formally enlist in any branch of the U.S. Military. Before she was commissioned as Chief Yeoman in 1917, women were hired as civilians by the military, and only as nurses. In 1917 the U.S. was preparing for what would become World War I, and not enough men were enlisting. This led to the authorization of women’s enlistment. Walsh was asked if she would be the first woman to serve in the Naval Reserve and she readily agreed. By putting on a male chief petty officer uniform (one she modified herself) and swearing the oath of enlistment, she opened the door for countless other women to follow in a more official capacity.

The Women of the 6888th Central Post Directory Battalion, US Women’s Army Corps

The 6888th was created to clear a heavy backlog of mail in Europe during World War II. Led by Lieutenant Colonel Charity Earley-Adams, the Six Triple Eight was the only all-black, all-female battalion sent overseas to support the war. Clearing 17 million pieces of mail was seen as a nearly impossible task. They were given six months and were not expected to succeed. The women of the 6888th worked in cold, rat-infested warehouses stacked to the ceiling with mail for U.S. service members. Despite discriminatory living conditions and a harsh working environment, they worked around the clock and got the job done in three months.

Colonel Eileen Collins, U.S. Air Force and NASA

Colonel Eileen Collins is a retired Air Force Colonel and retired NASA pilot. During her lengthy career, she broke through the glass ceiling of space—twice. In 1995, Collins became the first woman to pilot a space shuttle. In 1999, she was the first woman shuttle commander. She flew more than 5,000 hours in 30 different types of aircraft and logged 537 hours in space.

General Lori Robinson, U.S. Air Force

In 2016, General Lori Robinson became the highest-ranking woman in military history when she assumed command of NORAD and NORTHCOM. The highest-ranking officers in the Air Force were typically fighter pilots, which limited women from senior leadership career tracks until the Air Force allowed them to become fighter pilots, starting in 1993.

With her promotion in 2014, General Robinson became only the second woman in the history of the Air Force to hold the rank of general, and the first battlefield manager to do so. She was also chosen to lead Pacific Air Forces in Hawaii (PACAF), making her the first four-star woman in the U.S. Military to command combat forces.