Take off in military craft followed on radio (8)
I believe the answer is:
subtract
'take off' is the definition.
(synonyms)
'military craft followed on radio' is the wordplay.
'military craft' becomes 'sub' (submarine).
'followed' becomes 'tracked' (to track is to follow or tail).
'on radio' shows a homophone (sound like).
'tracked' sounds like 'tract'.
'sub'+'tract'='SUBTRACT'
'in' acts as a link.
(Other definitions for subtract that I've seen before include "Withdraw" , "Take an amount away" , "Remove" , "Take one quantity away from another" , "Knock off" .)