Officer needing a stout heart in the new army (5)
I believe the answer is:
mayor
'officer' is the definition.
(I've seen this before)
'a stout heart in the new army' is the wordplay.
'heart' means to look at the middle letters.
'in' means one lot of letters goes inside another.
'the new' is an anagram indicator.
The middle letter of 'stout' is 'o'.
'army' with letters rearranged gives 'mayr'.
'o' going into 'mayr' is 'MAYOR'.
'needing' acts as a link.
(Other definitions for mayor that I've seen before include "Municipal official" , "Corporation head" , "Town council head" , "City manager" , "Town chief" .)