http://www.uso.org/
Look it up, Yes it is Voluntary service to some entertainer's.
But not to the people who put on the show.
Welcome to The USO
The USO is a private, nonprofit organization whose mission is to support the troops by providing morale, welfare and recreation-type services to our men and women in uniform. The original intent of Congress — and enduring style of USO delivery — is to represent the American people by extending a touch of home to the military. The USO currently operates more than 130 centers worldwide, including ten mobile canteens located in the continental United States and overseas. Overseas centers are located in Germany, Italy, the United Arab Emirates, Japan, Qatar, Korea, Afghanistan, Guam, and Kuwait. Service members and their families visit USO centers more than 5.3 million times each year. The USO is the way the American public supports the troops.