The United Service Organizations has been working to boost American troops' morale since 1941. Though the USO provides a variety of services, it's most famous for its live shows that feature celebrities performing for U.S. service members wherever they're stationed. Over the decades, thousands of entertainers have performed in hundreds of thousands of USO-sponsored shows, most famously the late Bob Hope, who headlined 57 USO tours. In recent years, stars like Carrie Underwood, Stephen Colbert, Toby Keith, and late comedian Robin Williams have traveled to U.S. military bases in Afghanistan and Iraq to support the troops there. In doing so, they've upheld a proud American tradition. As we honor veterans, we look back at some rarely-seen photos and video clips showing the best known stars of the past decades doing their part to bring a bit of home to our G.I.s overseas.