American manoeuvres kept secret (2,6)
I believe the answer is:
in camera
'secret' is the definition.
(legal term meaning in private, lit. 'in a chamber')
'american manoeuvres' is the wordplay.
'manoeuvres' is an anagram indicator (letters manoeuvred in a new way).
'american' with letters rearranged gives 'IN CAMERA'.
'kept' is the link.
(Other definitions for in camera that I've seen before include "secretly" , "Kept private (law)" , "(Held) in private" , "without full scrutiny?" , "behind closed doors" .)