"The Silver Star is awarded to a person who, while serving in any capacity with the United States Armed Forces, is cited for gallantry in action against an enemy of the United States while engaged in military operations involving conflict with an opposing foreign force, or while serving with friendly foreign forces engaged in armed conflict against an opposing armed force in which the United States is not a belligerent party."

http://www.fact-index.com/s/si/silver_star.html