In armed force, gunners are at the forefront (3)
I believe the answer is:
raf
'in armed force' is the definition.
'RAF' can be an answer for 'force' (Royal Air Force). I'm not certain of the 'in armed' bit.
'gunners are at the forefront' is the wordplay.
'gunners' becomes 'RA' (Royal Artillery).
'are at' says to put letters next to each other.
'the forefront' becomes 'f' (this might be a standard abbreviation I've not previously seen).
'ra'+'f'='RAF'
Can you help me to learn more?
(Other definitions for raf that I've seen before include "It fought Battle of Britain" , "Royal Air Force (abbr.)" , "Airforce of Great Britain" .)