Irregular headed up military department after revolution (6)

I believe the answer is:
random
'irregular' is the definition.
(I've seen this before)
'headed up military department after revolution' is the wordplay.
'headed up' becomes 'ran' (I've seen this in another clue).
'military department' becomes 'mod' (I can't justify this - if you can you should believe this answer much more).
'after revolution' says the letters should be written in reverse (letters revolve back).
'mod' back-to-front is 'dom'.
'ran'+'dom'='RANDOM'
Can you help me to learn more?
(Other definitions for random that I've seen before include "Ill-planned" , "casual?" , "'Haphazard, irregular (6)'" , "Wild" , "Patternless" .)
