Special elite force about to take by assault (5)
I believe the answer is:
storm
'take by assault' is the definition.
(to storm a place is to take it by force)
'special elite force about to' is the wordplay.
'special' becomes 'S' (common abbreviation as in Special Air Service).
'elite force' becomes 'RM' (Royal Marines).
'about' says to put letters next to each other.
'rm' after 'to' is 'torm'.
's'+'torm'='STORM'
(Other definitions for storm that I've seen before include "Atmospheric disturbance, assault (stronghold)," , "commotion" , "Awful blow" , "violent assault" , "Rumpus" .)