Military man disposed of one facing Her Majesty (7)
I believe the answer is:
soldier
'military man' is the definition.
(soldier is a kind of military man)
'disposed of one facing her majesty' is the wordplay.
'disposed of' becomes 'sold' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'facing' is a charade indicator (letters next to each other).
'her majesty' becomes 'er' (Elizabeth Regina).
'sold'+'i'+'er'='SOLDIER'
(Other definitions for soldier that I've seen before include "Tommy Atkins or GI Joe?" , "Person serving in army" , "Military man" , "piece of toast" , "Member of the military" .)