Level of command in military formation (7)
I believe the answer is:
echelon
This clue is a double definition.
'level of command' is the first definition.
(I've seen this before)
'military formation' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for echelon that I've seen before include "Degree" , "Level or rank of authority, upper or lower" , "Level of people in organisation" , "Ladder formation" , "Bishops, say" .)