Really?
How do you come up with that deduction when he starts off the reply saying he'd just been discussing the issue before coming out to take questions?! That demonstrates he was
a) aware of the issue
and
b) fully prepared to address it which he proceeded to do in a lengthy, thoughtful and detailed answer.
I fail to detect "embarrasment" except the media's mischaracterization of his answer and there is zero evidence he was "caught off guard".
Your fierce defense of Rumsfeld only verifies my earlier remarks.
Do you really believe that he expected that question from the troops? I don't. He's good on his feet, but even the best can be surprised.