Upon taking the oath of office January 20, 2009, Barack Obama became the 44th president of the United States and commander in chief of the U.S. armed forces.
Under the U.S. Constitution, the military is subordinate to elected civilian leadership. Holding with tradition, the U.S. military honored its new commander by participating in the inaugural ceremonies and parade.
Below is a link to U.S. military activities related to the inauguration of the new president.
http://www.defenselink.mil/home/features/2009/0109_inauguration/