The most important six inches on the battlefield is between your ears.

We can kill lots of people. We do kill lots of people. We can destroy virtually anything we choose to destroy.

I think the core problem is much closer to recognizing where force is of value, where it is useful, and to distinguish that from situations in which war is not useful or is indeed counterproductive.

The most important six inches on the battlefield is between your ears.

General [James] Mattis's primary experience - indeed, his only experience - is as a member of the United States Marine Corps, where he served for 41 years. That's his experience.

The destruction that we have wreaked in the various theaters in which we've been engaged is really quite astonishing. But again, lethality, destruction, killing doesn't seem to achieve our objectives. So, my own sense is that a lack of lethality does not define the core problem.

We do everything humanly possible, consistent with military necessity, taking many chances to avoid civilian casualties, at all costs.