Crossword Genius

First characters assembled in military mess (5)

Ross

I believe the answer is:

snafu

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'mess' is the definition.
(thesaurus)

I cannot understand how the remainder of the clue works.

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(Other definitions for snafu that I've seen before include "Chaos (US slang)" , "Chaotic situation" , "Mess table" , "confused activity" , "Customary confusion" .)

I've seen this clue in The Guardian.
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