Soldier possibly joins wife before heading back for port (7)
I believe the answer is:
antwerp
'port' is the definition.
(Belgian port)
'soldier possibly joins wife before heading back' is the wordplay.
'soldier possibly' becomes 'ant' (as in army ants).
'joins' is a charade indicator (letters next to each other).
'wife' becomes 'w'.
'before' becomes 'pre' (prefix meaning 'before').
'heading back' is a reversal indicator.
'pre' back-to-front is 'erp'.
'ant'+'w'+'erp'='ANTWERP'
'for' acts as a link.
(Other definitions for antwerp that I've seen before include "Belgian port and province" , "War-damaged city" , "Busy Belgian port" , "harbour" , "Major European port" .)