Some ammunition for a body of troops (4)
I believe the answer is:
unit
'a body of troops' is the definition.
(I've seen this in another clue)
'some ammunition for' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'UNIT' can be found hidden inside 'ammunition for'.
(Other definitions for unit that I've seen before include "Kitchen fitment" , "Single whole as part of a larger whole" , "Standard for measuring" , "A single, complete item" , "Part of a kit" .)