Ashton Carter has an unusual background for a secretary of defense. Before assuming the United States’ top military post in February, he studied medieval history and particle physics as an undergraduate at Yale, got a Ph.D. in physics as a Rhodes scholar at Oxford, and taught international affairs at Harvard. He also served as an assistant secretary of defense in the Clinton administration and as an undersecretary and then the deputy secretary of defense under President Barack Obama. Since becoming secretary, Carter has displayed an unusual bluntness, openly criticizing Iraq’s military forces and talking tough to adversaries such as China and Russia. In his first full-length print interview since becoming secretary, Carter met with Foreign Affairs managing editor Jonathan Tepperman in his Pentagon office in early July.

You’ve held a lot of jobs in the course of your career. Which best prepared you for your current position?

I would say that what has prepared me best is seeing, over several decades, some of the very best of my predecessors in action. My other previous jobs have been more managerial and in the technology area, which means that I know how things work here.

And all this helps me do the things I’m most intent on doing as secretary of defense. Those are, first of all, taking care of our troops. I learned from all [my predecessors] that I have a tremendous fiduciary duty toward the troops. They’re what I wake up to in the morning.

The other thing is to help the president make the difficult decisions about our foreign policy and carry out that part of it which involves the weight of the greatest fighting force the world has ever known.

And the last thing I keep uppermost in my mind is the future of this institution and making sure that we continue to have the very best people in our all-volunteer force, that we have the very best technology, and that we continue to