Weapon providing gunners with support (6)
I believe the answer is:
rapier
'weapon' is the definition.
(rapier is a kind of weapon)
'gunners with support' is the wordplay.
'gunners' becomes 'RA' (Royal Artillery).
'with' is a charade indicator (letters next to each other).
'support' becomes 'pier' (type of structure).
'ra'+'pier'='RAPIER'
'providing' is the link.
(Other definitions for rapier that I've seen before include "Light sword" , "Thin sharp sword" , "A thin double-edged sword" , "A small spring flower" , "Thrusting weapon" .)