Reach for the soldiers, in a box (6)
I believe the answer is:
attain
'reach' is the definition.
(I know that reach can be written as attain)
'soldiers in a box' is the wordplay.
'soldiers' becomes 'TA' (abbreviation for Territorial Army).
'in' means one lot of letters goes inside another.
'box' becomes 'tin' (I've seen this in other clues).
'a'+'tin'='atin'
'ta' inserted into 'atin' is 'ATTAIN'.
'for the' is the link.
(Other definitions for attain that I've seen before include "Reach objective or ambition" , "Reach, get there as with ambition" , "Reach or accomplish" , "Reach (a specified level)" , "Achieve or accomplish" .)