Gunners return to lines with weapons (6)
I believe the answer is:
arrows
'weapons' is the definition.
(arrow is a kind of weapon)
'gunners return to lines' is the wordplay.
'gunners' becomes 'ra' (Royal Artillery).
'return' says the letters should be written in reverse.
'to lines' becomes 'rows' (row is a kind of line**).
'ra' back-to-front is 'ar'.
'ar'+'rows'='ARROWS'
'with' acts as a link.
(Other definitions for arrows that I've seen before include "Bolts that are shot" , "''To suffer the slings and ... of outrageous fortune'' (Hamlet)" , "Marks to show direction" , "Quarrels, for example" , "Archers shafts" .)