Attack with ultimate in air support (4)
I believe the answer is:
raid
'attack' is the definition.
(raid is a kind of attack)
'with ultimate in air support' is the wordplay.
'with' means one lot of letters go next to another.
'ultimate in' indicates one should take the final letters.
'support' becomes 'aid' ('aid' can be a synonym of 'support'**).
The last letter of 'air' is 'r'.
'r'+'aid' is 'RAID'.
(Other definitions for raid that I've seen before include "Sally" , "Stock Exchange activity" , "A sudden attack or incursion" , "Invasion" , "Foray, sudden attack" .)