Order to begin shooting war (6)
I believe the answer is:
action
I believe this is a double definition.
'order to begin shooting' is the first definition.
(as in 'action' on a film set)
'war' is the second definition.
(action can mean action in war)
(Other definitions for action that I've seen before include "Law suit" , "war?" , "Director's cue?" , "Not CIA (anag)" , "exploit" .)