Tango is part of the phonetic alphabet. That way when you are on the radio, you can spell something out and you won't get the letters confused. Like I may say "T" on the radio and you might thing that I was saying "C'. So tango is for "T".
Sometimes some unites use the word "Tango" to mean target. Like they eliminated the target, or the "Tango" (target) is on the move.
As for Generation Kill, they used "Tango" a lot when they were referring to a couple of the guys as "Whiskey Tango", which stood for white trash. They took the intials of white trash "WT" and applied the phonetic alphabet, "Whiskey Tango". That was used a lot in Generation Kill, which is a damn good show...lol