Men infiltrating Native American city (7)
I believe the answer is:
toronto
'american city' is the definition.
(I've seen this before)
'men infiltrating native' is the wordplay.
'men' becomes 'OR' (Other Ranks: non-commissioned soldiers).
'infiltrating' is an insertion indicator.
'native' becomes 'tonto' (I can't justify this - if you can you should believe this answer much more).
'or' going into 'tonto' is 'TORONTO'.
Can you help me to learn more?
(Other definitions for toronto that I've seen before include "major city" , "Largest city in Canada" , "Canadian city" , "Canada's largest city" , "North American city" .)