Warplane circling about does for cargo ship (9)
I believe the answer is:
freighter
'for cargo ship' is the definition.
(freighter is a kind of cargo ship)
'warplane circling about' is the wordplay.
'warplane' becomes 'fighter' (I've seen this before).
'circling' indicates putting letters inside (circling can mean going around or containing).
'about' becomes 're' (regarding).
'fighter' placed around 're' is 'FREIGHTER'.
'does' is the link.
(Other definitions for freighter that I've seen before include "Cargo-ship" , "Cargo ship" , "transport vessel" , "Cargo-carrying ship or plane" , "A plane carrying large load" .)