State of planes in navy manoeuvres (12)
I believe the answer is:
pennsylvania
'state' is the definition.
(Pennsylvania is an example)
'planes in navy manoeuvres' is the wordplay.
'manoeuvres' indicates an anagram.
'planes'+'in'+'navy'='planesinnavy'
'planesinnavy' is an anagram of 'PENNSYLVANIA'.
'of' is the link.
(Other definitions for pennsylvania that I've seen before include "State of NE US" , "State of northeastern US" , "State of NE? USA" .)