Eccentric involved in defending battleships (7)
I believe the answer is:
dingbat
'eccentric' is the definition.
'involved in defending battleships' is the wordplay.
'involved in' indicates the answer is hidden within the clue.
'DINGBAT' is hidden within 'defending battleships'.
(Other definitions for dingbat that I've seen before include "funny-looking character" , "Aussie fool" , "Simpleton" , "Silly billy - it'd bang (anag)" , "Eccentric person" .)