Leon Panetta on Friday took over as the new Defence Secretary, pledging to keep the American forces the "strongest" in the world.
"As your leader, I will ensure that our nation continues to have the best-trained, best-equipped, and strongest military in the world - a force prepared to confront the challenges that face us," Panetta said in a message to the armed forces soon after being sworn in as the 23rd US Defense Secretary.
Department of Defence General Counsel Jeh Johnson administered the oath of office to Panetta, who succeeds Robert Gates.
"As CIA Director, I saw first-hand the tremendous capabilities of our military, and I was always impressed by the professionalism and patriotism of the men and women of the Armed Forces," said the 73-year-old, who resigned from the CIA to take the top Pentagon job.
"Our nation is at war. We must prevail against our enemies. We will persist in our efforts to disrupt, dismantle, and ultimately defeat al Qaeda.
The successful operation that killed Osama Bin Laden -a mission that showcased American military strength and precision - is a major step toward that goal," said the new Pentagon chief.