Relief for troops taking part in struggle (6)
I believe the answer is:
effort
'struggle' is the definition.
(I've seen this before)
'relief for troops taking part' is the wordplay.
'taking part' indicates the answer is hidden within the clue.
'EFFORT' can be found hidden inside 'relief for troops'.
'in' acts as a link.
(Other definitions for effort that I've seen before include "Vigorous attempt" , "Strenuous exertion" , "Struggle" , "Endeavour, elbow grease" , "Exertion, elbow grease" .)