Some soldiers not exactly right to return ammunition (6)
I believe the answer is:
tracer
'ammunition' is the definition.
(tracer is a kind of ammunition)
'some soldiers not exactly right to return' is the wordplay.
'some soldiers' becomes 're' (Royal Engineers).
'not exactly' becomes 'ca' (circa).
'right' becomes 'rt'.
'to return' shows that the letters should be reversed in order.
're'+'ca'+'rt'='recart'
'recart' back-to-front is 'TRACER'.
(Other definitions for tracer that I've seen before include "Type of bullet or shell" , "Kind of bullet that leaves trail" , "ammunition" , "Projectile" , "beast to tow" .)