I think I know what they might be hinting at, in a way, by the words "tango", "echo", and "x-ray". (As it is, I'm not sure my insight will be all that helpful.)
This may sound really stupid, but I'm positive that those code words are all taken from the military alphabet. Which, (partly because of the part the military plays in my relative's lives, partly because it's an interesting subject, and partly because memorizing the alphabet was fun), I decided to do a brief study on.
First, here's a handy link to the wikipedia page on it:
http://en.wikipedia.org/wiki/Military_alphabet
Anyway, the NATO alphabet is used in the military so that code words assigned to different letters of the alphabet don't get mixed up over telephone or radio communication. (e.g. "B" and "D" sort of sound alike.) I don't know what the code words are, but I'm guessing they aren't the same for every mission. So, yeah. That's my thoughts on the subject.

I believe that Tango is indeed an Americanism, as I've seen it used in books I've read about the Navy SEALs. Fraid I can't help you with the rest, though.