Gunners get support weapon (6)
I believe the answer is:
rapier
'weapon' is the definition.
(rapier is a kind of weapon)
'gunners get support' is the wordplay.
'gunners' becomes 'ra' (Royal Artillery).
'get' says to put letters next to each other.
'support' becomes 'pier' (pier is a kind of support**).
'ra'+'pier'='RAPIER'
(Other definitions for rapier that I've seen before include "Straight sword with narrow blade" , "A fencing sword for repair" , "Fine-bladed sword" , "Straight narrow sword with two edges" , "fencing equipment" .)