The United Service Organizations, Inc. (USO) has been working to boost American troops' morale since 1941, when President Franklin D. Roosevelt proposed the idea for such a group. Though the USO provides a variety of services, it's most famous for its live "Camp Shows" that bring celebrities to perform for service members wherever they're stationed. Over the decades, thousands of entertainers have performed hundreds of thousands of USO-sponsored shows. The late Bob Hope was well known for his USO service, and in recent years, stars like Carrie Underwood, Stephen Colbert, Toby Keith, and Sen. Al Franken 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. This month, we celebrate the annual USO Day (Feb. 4) with a look back at some rarely-seen photos and video clips showing the best known stars of the '40s, '50s, '60s and '70s doing their part to bring a bit of home to our G.I.s overseas.