Heavy guns and military supplies (8)
I believe the answer is:
ordnance
'heavy guns and military supplies' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ordnance that I've seen before include "Heavy guns and military supplies" , "Military supplies and materials" , "Car on end (anag) - artillery" , "weapons" , "Department concerned with artillery" .)