Area by border invaded by servicemen in WWII battle (6)
I believe the answer is:
arnhem
'battle' is the definition.
(the Battle of Arnhem was a WW2 battle)
'area by border invaded by servicemen' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'by' says to put letters next to each other.
'border' becomes 'hem' (I've seen this before).
'invaded by' means one lot of letters goes inside another.
'servicemen' becomes 'RN' (abbreviation for Royal Navy).
'a'+'hem'='ahem'
'ahem' enclosing 'rn' is 'ARNHEM'.
'in wwii' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for arnhem that I've seen before include "Location of battle" , "Netherlands scene of 1944 battle" , "place noted for fighting" , "Site of 1944 battle" , "Second World War battle" .)