Some soldiers can return to university (4)
I believe the answer is:
unit
'some soldiers' is the definition.
(unit can mean a group of soldiers )
'can return to university' is the wordplay.
'can' becomes 'tin' (both are metal containers).
'return' is a reversal indicator.
'to' means one lot of letters go next to another (I've seen this in other clues).
'university' becomes 'U' (abbreviation for university).
'tin' written backwards gives 'nit'.
'nit' after 'u' is 'UNIT'.
(Other definitions for unit that I've seen before include "Single item, maybe part of a set" , "Subdivision of a military group" , "Single element; one" , "Kitchen element?" , "Specialised group" .)