Small body of soldiers also included in scheme (7)
I believe the answer is:
Here is my best explanation:
'small body of soldiers' is the definition.
(I've seen this before)
'also included in scheme' is the wordplay.
'also' becomes 'too' ('too' can be a synonym of 'also').
'included in' means one lot of letters goes inside another.
'scheme' becomes 'plan' (I've seen this before).
'too' going inside 'plan' is 'PLATOON'.
(Other definitions for platoon that I've seen before include "Group of soldiers", "Infantry unit", "Military group", "Small body of soldiers", "Subdivision of a company", "Army unit", "part of company", "Sub-unit of a military company", "Unit" and "detail".)