Military group with unknown togetherness (5)
I believe the answer is:
unity
'togetherness' is the definition.
(I've seen this before)
'military group with unknown' is the wordplay.
'military group' becomes 'unit' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'unknown' becomes 'y' (algebra).
'unit'+'y'='UNITY'
(Other definitions for unity that I've seen before include "Accord" , "One of the Mitfords" , "State of togetherness" , "Mitford girl" , "One - mutual agreement" .)