Men turned up in leading company (5)
I believe the answer is:
troop
'company' is the definition.
(I've seen this before)
'men turned up in leading' is the wordplay.
'men' becomes 'or' (I've seen this in other clues).
'turned up' is a reversal indicator.
'in' means one lot of letters goes inside another.
'leading' becomes 'top' (**).
'or' back-to-front is 'ro'.
'ro' going inside 'top' is 'TROOP'.
(Other definitions for troop that I've seen before include "Body of soldiery" , "(Of people) come or go in large numbers" , "Military group" , "Group of kangaroos" , "Military unit" .)