Deploy a lunatic marine (8)
I believe the answer is:
nautical
'marine' is the definition.
('nautical' can be a synonym of 'marine')
'deploy a lunatic' is the wordplay.
'deploy' is an anagram indicator (I've seen 'deployed' mean this).
'a'+'lunatic'='alunatic'
'alunatic' with letters rearranged gives 'NAUTICAL'.
(Other definitions for nautical that I've seen before include "Maritime" , "A lunatic about sailors or seamanship" , "Relating to sailors" , "Relating to ships and sailing" , "Of ships and navigation" .)