Service held in (clears throat) site of Monty's overreach (6)
I believe the answer is:
arnhem
'clears throat site of monty's overreach' is the definition.
I can't tell whether this defines the answer.
'service held in' is the wordplay.
'service' becomes 'RN' (abbreviation for Royal Navy).
'held' becomes 'ahem' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'rn' put inside 'ahem' is 'ARNHEM'.
Can you help me to learn more?
(Other definitions for arnhem that I've seen before include "Second World War battle" , "WW2 battle" , "place noted for fighting" , "Location of battle" , "Netherlands scene of 1944 battle" .)