Wartime offensive a cause of radio silence? (3,6)
I believe the answer is:
air strike
'wartime offensive' is the definition.
(type of offensive action in war)
'radio silence?' is the wordplay.
'radio' becomes 'air' (I've seen this before).
'silence?' becomes 'strike' (I can't justify this - if you can you should give a lot more credence to this answer).
'air'+'strike'='AIR-STRIKE'
'a cause of' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for air strike that I've seen before include "Bombing attack" , "shot from above" , "makes flight impossible?" .)