Some immunity for soldiers (4)
I believe the answer is:
unit
'soldiers' is the definition.
(unit can mean a group of soldiers )
'some immunity 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 within 'immunity for'.
(Other definitions for unit that I've seen before include "Single undivided whole" , "Single piece - kitchen cabinet" , "Single whole as part of a larger whole" , "Individual component" , "1 entity" .)