The most famous American woman to “serve” during World War II didn’t actually exist.

But the hundreds of thousands of women who Rosie the Riveter came to symbolize did. For more than four years, they were the not-so-secret weapon that kept the country and the war effort going.

Not long after the U.S. entered the war in December 1941, the War Manpower Commission was created. Its goal: ensuring the country's labor needs could be met with male workers off fighting.Womanpower seemed the logical answer.

It wasn’t as simple as posting on LinkedIn, though. In 1940, the U.S. workforce was only 27 percent female, mostly single women in more “traditional” clerical or teaching jobs. So the government had to persuade more women to join the workforce and employers to get on board. One company, Westinghouse Electric, hired an artist to create employee morale-boosting posters. One memorably depicted a working woman flexing her muscle and boasting “We Can Do It!” A song about “Rosie the Riveter” already existed, and as similar images began popping up (including one by Norman Rockwell), an inspirational symbol was born.

So was a new reality: By 1945, women comprised 37 percent of the workforce, and nearly one in four married women worked outside the home. That included 310,000 women — 65 percent of all employees, versus just 1 percent before the war — in the crucially important U.S. aircraft industry. Meanwhile, 350,000 women joined the armed services, including 100,000 Women’s Army Corps (WAC) members and some 1,000 WASPs. These female pilots’ duties included flying military planes from factories to bases so their male Air Force counterparts could fly combat missions.

When the war was over and the men returned to civilian life, many of these women lost their jobs. But they and “Rosie” — who has since gone on to become an iconic feminist image — had kicked open a door for future generations.