First characters assembled in military mess (5)
I believe the answer is:
snafu
'mess' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for snafu that I've seen before include "Chaos (US slang)" , "Chaotic situation" , "Mess table" , "confused activity" , "Customary confusion" .)