German forces arrange the march west (9)
I believe the answer is:
wehrmacht
'german forces' is the definition.
'arrange the march west' is the wordplay.
'arrange' indicates an anagram.
'west' becomes 'w' ('W' can be a synonym of 'west').
'the'+'march'+'w'='themarchw'
'themarchw' is an anagram of 'WEHRMACHT'.
(Other definitions for wehrmacht that I've seen before include "Allies' enemy" , "German armed forces nineteen twenty one to nineteen forty five" , "German forces (nineteen twenty-one to nineteen forty-five)" , "army" .)