Grades lines of soldiers (5)
I believe the answer is:
ranks
This clue is a double definition.
'grades' is the first definition.
(rank can mean a grade or level)
'lines of soldiers' is the second definition.
(rank can mean a group of soldiers in a line)
(Other definitions for ranks that I've seen before include "Positions of seniority" , "Classifies" , "Series of soldiers" , "Lines or rows of people or things" , "Rows (of soldiers)" .)