Be polite, be professional, but have a plan to kill everyone you meet.

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

Since 9/11 we've been engaged in wars around the world, and General [James] Mattis has been a leading battlefield commander in many of those theaters, including in the April 2004 siege of Fallujah, where the US Marines killed so many people that the municipal soccer stadium in the city had to be turned into a graveyard for the dead.

It is mostly a matter of wills. Whose will is going to break first? Ours or the enemy's?

In this age, I don't care how tactically or operationally brilliant you are, if you cannot create harmony - even vicious harmony - on the battlefield based on trust across service lines, across coalition and national lines, and across civilian/military lines, you need to go home, because your leadership is obsolete. We have got to have officers who can create harmony across all those lines.

What would you do differently as defense secretary to compensate for this record in which the greatest military in the world, as we are constantly told, doesn't get the job done?

I just hope we can find our way back to engaging with one another, arguing strongly with one another, and then going down and having a root beer together or something and - and having a good laugh about it as we work together for the best interests of the next generation of Americans who are going to inherit this country.