Military group also in scheme (7)
I believe the answer is:
platoon
'military group' is the definition.
(I've seen this before)
'also in scheme' is the wordplay.
'also' becomes 'too' (synonyms).
'in' means one lot of letters goes inside another.
'scheme' becomes 'plan' (I've seen this before).
'too' put within 'plan' is 'PLATOON'.
(Other definitions for platoon that I've seen before include "Company's subdivision" , "detail" , "Group under lieutenant" , "Subdivision of a company" , "Team under lieutenant" .)