Part of Beaverbrook in a war's campaign (7)
I believe the answer is:
okinawa
'campaign' is the definition.
(Okinawa is an example)
'part of beaverbrook in a war's' is the wordplay.
'part of' indicates a hidden word.
'OKINAWA' is hidden in the letters of 'beaverbrook in a wars'.
(Other definitions for okinawa that I've seen before include "island out east" , "Island of S. Japan" , "battle!" , "Pacific island" , "Japanese island, capital Naha" .)