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 subsidiary indication.
'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' put into 'plan' is 'platoon'.
(Other definitions for platoon that I've seen before include "Sub-unit of a military company", "Small body of soldiers", "Military subunit", "Group under lieutenant", "Squad", "Military group", "Soldiers under lieutenant", "Military unit", "Small military unit" and "Group of soldiers".)