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