MILWAUKEE – When Anna Mae Robertson and her fellow soldiers arrived in England early in 1945, millions of pieces of mail and parcels destined for homesick American troops gathered dust in postal bags piled high in warehouses.

Knowing the importance to morale of letters and packages from home, commanders gave the difficult task of sorting through a months-long backlog of mail to the Women's Army Corps 6888 Central Postal Directory Battalion. The women devised a system, rolled up their sleeves and got to work.

"We worked in shifts around the clock. You had to find the right name and address," Robertson, 95, recalled in a recent interview at her Milwaukee home. "You just managed."

The hard work and critical role played by the battalion of African American women during World War II is spotlighted in a new documentary by a filmmaker from Wisconsin. Jim Theres filmed interviews with the last seven survivors of the unit for his documentary, "The Six Triple Eight," which will be shown at the War Memorial Center in Milwaukee on June 6.

Robertson was interviewed for the documentary and will appear at the screening.

Memorial Day deals:Free food and Memorial Day deals for active military and veterans Monday

Record number of black female grads:West Point's class of 2019 includes historic number of African-American women

Arriving in Birmingham, England, in February 1945 after their convoy across the Atlantic was rerouted because of German U-boats, postal battalion soldiers quickly organized a system to find troops who had been on the march since the D-Day invasion. Some letters were simply addressed "Junior, U.S. Army," rats and mice had gnawed into parcels packed with baked goods, and tracking down the 7 million American GIs in Europe was incredibly difficult.

But the 855 women in the Six Triple Eight figured it out, processing 65,000 pieces of mail during each eight-hour shift. They worked in unheated buildings with windows darkened because of nightly attacks by German pilots and V-2 rockets. Some of the women were assigned the sad task of returning mail sent to troops killed before their letters from home reached them.

The six-month backlog was cleared in half the time. Since the Army was still segregated, they lived and ate in barracks apart from other American soldiers with battalion members assigned to handle their own motor pool and chow hall.

"These are the stories that got stuck in the nooks and crannies of history. When people hear about this, their reaction is almost universally the same: 'Wow, I didn't know about that,'" said Theres, a Racine native.

Theres was screening a documentary last year on American female telephone operators in Europe during World War I when someone in the Milwaukee audience asked if he knew about the all-African American female postal battalion. He Googled the unit, was amazed to learn its story and decided to make a documentary.

All seven surviving veterans Theres could track down agreed to take part in the movie. He recorded five of the interviews, including Robertson's, in November during ceremonies in Fort Leavenworth, Kansas, dedicating a monument to the 6888 Postal Battalion.

Theres wondered if the women would talk about the racism and sexism they experienced at home and in the military.

"But they talked about the good things that happened in Birmingham (England), their sense of mission, how proud they were to find homes for millions of pieces of mail," Theres said. "That was their focus. That made the conversations just so engaging. It was really wonderful."

At the start of the war, only 10% of the Women's Army Corps at any one time could be African American. Black female soldiers began calling themselves the "10 percenters."

They fought Nazis, now they fight rust:Veterans struggle to save World War II ships

WWII vet battles dementia:Family's research uncovers lost stories from the veteran's life

The military also restricted the number of black female officers with each branch to one full colonel or Navy captain. More than 6,500 African American women served in the Women's Army Corps throughout World War II. In 1948, America's military was integrated.

Marcia Anderson, the first African American woman to become a major general in the Army, knew about the 6888th as she made a career in the military.

The Six Triple Eight is "something that's passed down among black female officers," said Anderson, a Beloit native who is now clerk of court for the U.S. Bankruptcy Court in Wisconsin's Western District. "I definitely stand on their shoulders."

Anderson, who was interviewed for the documentary, knows the importance of communication to military members trying to connect with family and friends while serving so far from home, whether it was letters and parcels during World War II or email, text messages and care packages for today's troops.

"Back in the day when there wasn't email, mail call was a significant event. To learn that all that mail was sitting around in warehouses in England is incomprehensible," said Anderson.

Mike Pence at West Point commencement:Praises for Trump, graduates' diversity

In June 1945, the unit was sent to France where it worked on another backlog of mail alongside French civilians and German POWs. The next month, three soldiers in the battalion were killed in a Jeep crash and were buried in the cemetery made famous in the film "Saving Private Ryan."

Since the War Department didn't pay for their funerals, fellow 6888th soldiers pooled their money to buy caskets, and three women in the unit with mortuary experience took care of the bodies.

Early in 1946, the unit returned to the U.S. from France and was quietly disbanded. There were no parades, no recognition, no medals.

A native of Mississippi, Robertson, whose maiden name is Wilson, was living in Arkansas when her mother died. She was 19 and had no way to support herself, so she decided to join the Army in March 1943.

Robertson came to Milwaukee after the war for the wedding of a fellow soldier and decided to stay here. She got a job as a nurse's aide at the VA hospital, married in 1948 and raised eight children, including a daughter who worked for the U.S. Postal Service.

She didn't talk much about her service in World War II and quietly raised her family, instilling in them a sense of duty and the importance of education, said her daughter Sheree Robertson.

Vets' donation saves 4-year-old:Army veteran meets the little girl he saved with his bone marrow donation

"As she journeyed through life, she continued to be a courageous woman. She worked hard and raised her eight children to make good choices and let their light shine," Sheree Robertson said.

Not until 2014, with the intervention of Congresswoman Gwen Moore, D-Wis., did Robertson finally receive the Women's Army Corps Medal, American Campaign Medal, European-African-Middle Eastern Campaign Medal, World War II Victory Medal and the Honorable Service Lapel Button WW2.

The medals are in a shadow box that Robertson proudly hangs on a wall in her home.

Follow Meg Jones on Twitter: @MegJonesJS