Also in the scheme as a unit (7)
I believe the answer is:
platoon
'a unit' is the definition.
(platoon is a kind of unit)
'also in the scheme' is the wordplay.
'also' becomes 'too' ('too' can be a synonym of 'also').
'in the' indicates putting letters inside.
'scheme' becomes 'plan' (I've seen this before).
'too' inserted into 'plan' is 'PLATOON'.
'as' is the link.
(Other definitions for platoon that I've seen before include "Soldiers under lieutenant" , "Team under lieutenant" , "Military group" , "Army unit" , "Subdivision of a company" .)