Rogue operations primarily expand ex-US base (7)
I believe the answer is:
roswell
'ex-us base' is the definition.
(Walker Air Force Base also known as Roswell)
'rogue operations primarily expand' is the wordplay.
'primarily' suggests taking the first letters.
'expand' becomes 'swell' (swelling is a kind of expanding).
The first letters of 'rogue operations' is 'ro'.
'ro'+'swell'='ROSWELL'
(Other definitions for roswell that I've seen before include "New Mexico city" , "town in New Mexico" .)