Suddenly attack outpost or military enclosure (5)
I believe the answer is:
storm
'suddenly attack' is the definition.
'storm' can be an answer for 'attack' (storm can mean to take by force). I am not certain of the 'suddenly' bit.
'outpost or military enclosure' is the wordplay.
'STORM' is hidden within the letters.
However, I'm not sure how this is indicated.
Can you help me to learn more?
(Other definitions for storm that I've seen before include "Wind force 10 on Beaufort scale" , "Rampage" , "rage" , "Awful blow" , "X-Men character" .)