Some ammunition for military detachment (4)
I believe the answer is:
unit
'military detachment' is the definition.
(I've seen this in another clue)
'some ammunition for' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'UNIT' is hidden in the letters of 'ammunition for'.
(Other definitions for unit that I've seen before include "army group" , "One part of a whole" , "Single thing or person" , "Small military detachment" , "Single manufactured item; military grouping" .)