Editor's note: This piece was co-athored by Greg Jaffe

Leon Panetta, sworn in Friday as the nation’s 23rd secretary of defense, pledged that there would be “no hollow force on my watch,” as the Pentagon seeks to rein in costs without undermining military readiness.

In an opening message to Defense Department personnel, Panetta acknowledged the fiscal challenges he is inheriting, including an administration request to identify $400 billion in savings from the defense budget over the next 12 years. But Panetta also said that he believes in achieving a balance between disciplined spending and doing what is necessary to protect U.S. forces.