Military operation bringing gunners to a horrid end (4)
I believe the answer is:
raid
'military operation' is the definition.
(a military attack)
'bringing gunners to a horrid end' is the wordplay.
'bringing gunners' becomes 'rai' (I can't explain this - if you can you should give a lot more credence to this answer).
'end' indicates one should take the final letters.
The last letter of 'horrid' is 'd'.
'rai'+'d'='RAID'
Can you help me to learn more?
(Other definitions for raid that I've seen before include "Enter a territory and take spoils" , "Search by police without warning" , "Sudden short attack" , "bust" , "A sudden military attack and withdrawal" .)