Adm. Mike Mullen (left), Defense Secretary Leon E. Panetta (center) and Vice President Joseph R. Biden Jr. stand during the playing of the national anthem at the Pentagon in Arlington on Sunday, Sept. 11, 2011, the 10th anniversary of the Sept. 11 attacks. (AP Photo/Charles Dharapak)

Photo by: Charles Dharapak

Adm. Mike Mullen (left), Defense Secretary Leon E. Panetta (center) and Vice President Joseph R. Biden Jr. stand during the playing of the national anthem at the Pentagon in Arlington on Sunday, Sept. 11, 2011, the 10th anniversary of the Sept. 11 attacks. (AP Photo/Charles Dharapak)