Organise an army unit (8)
I believe the answer is:
regiment
This clue is a double definition.
'organise' is the first definition.
(I know that regiment is a more specific form of the action organise)
'an army unit' is the second definition.
(I know that regiment is a type of army unit)
(Other definitions for regiment that I've seen before include "Part of an army" , "a whole lot of them" , "Military group" , "subject to excessive control" , "Army group" .)