Militarise division (3)
I believe the answer is:
arm
This clue is a double definition.
'militarise' is the first definition.
(I've seen this in another clue)
'division' is the second definition.
(I know that arm is a type of division)
(Other definitions for arm that I've seen before include "Shoulder-to-wrist member" , "Limb or branch" , "Steel" , "Shoulder to fingertip" , "Activate warhead" .)