Although the classic Gibson guitar, used by such greats as Prince, Keith Richards, Johnny Cash, and B.B. King, might bring to mind its current Nashville home, the guitar’s roots are actually in the Michigan city of Kalamazoo. Built in 1917, the Gibson Factory there created some of the most iconic guitars ever made. But beyond the instruments, the factory was also home to the “Kalamazoo Gals,” a group of over 200 women who kept the guitar manufacturer going during World War II.

Started by local mandolin designer Orville Gibson in 1902, the Gibson company was the place for discerning mandolin players to get their instruments. The only thing that slowed the company down during its first decade was World War I. As men were being shipped off to battlefields, the demand for the instrument began to diminish. And although it had been popular with both men and women, the country’s attentions were decidedly not focused on the mandolin anymore.

It also didn’t help that upon returning home, the sweet, soft sounds of the mandolin were not what these soldiers wanted to hear. They’d moved on to jazz, and the mandolin just wasn’t going to keep up with that energy. The company tried to redesign the instrument, make it hip again, but no success. The company knew that to hang on to their customers, it needed to give them something else. This began the new era of guitar making. Unfortunately, World War II happened soon after.

With the ongoing war, many of Gibson’s competitors had switched from instrument-making to munition-making in their effort to support the war at home. Gibson joined suit, well, sort of. With the men gone, the factory began hiring women to make munitions. In fact, between 1942 and 1946, it hired more women than any other guitar-turned-munitions manufacturer.

But secretly, these women weren’t just making bullets. They were making guitars. The Kalamazoo Gals made Gibson’s Banner line of guitars, “acoustic guitars had a gold banner on the headstock with the slogan, ‘Only a Gibson is Good Enough’.” These guitars were made until the end of the war, and used by musicians like Buddy Holly and Woody Guthrie.

But the existence of the Kalamazoo Gals stayed a secret long after the war ended, only coming to light in recent years through a little deep digging from writer John Thomas who discovered “almost 25,000 instruments shipped during the war.” When the men returned from the war, everything at the Gibson factory went back to business as usual, leaving the women of Gibson an (almost) forgotten piece of music history.

Ultimately, in 1985 the Gibson factory left Kalamazoo and headed for Nashville. However, a few Gibson employees stayed behind and created Heritage Guitar on the site of the old Gibson factory, so Kalamazoo’s rich history of instrument-making lives on. Today, the site is open for tours, and an upcoming renovation and partnership with Rolling Stone plans to make it a destination for music lovers.