Group of soldiers also included in scheme (7)
I believe the answer is:
Here is my best explanation:
'group 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' indicates putting letters inside.
'scheme' becomes 'plan' (I've seen this before).
'too' put within 'plan' is 'platoon'.
(Other definitions for platoon that I've seen before include "Group under lieutenant", "Military unit", "Soldiers under lieutenant", "Army unit", "Group of soldiers", "Sub-unit of a military company", "Military group", "Small body of soldiers", "Subdivision of a company" and "Military squad".)