About military intelligence, is naive (5)
I believe the answer is:
green
'naive' is the definition.
(similar in meaning)
'about military intelligence' is the wordplay.
'about' indicates putting letters inside.
'military' becomes 're' (I've seen this in other clues).
'intelligence' becomes 'gen'.
're' inserted inside 'gen' is 'GREEN'.
'is' acts as a link.
(Other definitions for green that I've seen before include "The colour of inexperience" , "Not yet ripe" , "Grassy enclosure, in a village say" , "Caring for environment" , "Fresh - environmentally friendly - colour" .)