Marches; army (6)
I believe the answer is:
troops
This clue is a double definition.
'marches' is the first definition.
(trooping is a kind of marching)
'army' is the second definition.
(I've seen this before)
(Other definitions for troops that I've seen before include "Army" , "Military forces" , "men" , "Soldiers, armed forces" , "Cavalry" .)