In the rainbow six computer game (and I think Sum of All fears), the counter terrorists say ‘tango down’ when taking out one of the enemies, to tell the others what’s happening, Is this a real phrase, used by counter-terrorists and if so (or if not, even), what does it mean?
The two games I mentioned are both based on Tom Clancy books, although sum of All fears may be more inspired by the film. Both I gather have Tom Clancy’s in front of the name. So that suggests another question, that of whether the phrase crops up in other Tom Clancy stuff, such as his books, or films.
tango= T
T-errorist
for operation security reasons you would change code words for each mission
Really nothing special about it. “Tango” is T in the phonetic alphabet and is often used as shorthand for “target.” All tango down means is target down (shot/disabled).
We were using “tango down” in MOUT training when I was in the infantry in the early 90s.
Military Operations on Urbanized Terrain, for those of you scratching your heads. Fighting in a city.
Darn, I thought you were referring to relatives of ROUS 
I don’t mean to be a smartass, but how is tango short for target, since they’re the same number of syllables?
Tango is the standard military phonetic code for the letter T.
A= Alpha, B= Bravo, etc… etc
The “word for the letter” is chosen on the basis of uniqueness or non-ambiguity.