Bombed fort vanished quickly (4,4,4)
I believe the answer is:
hand over fist
'quickly' is the definition.
(thesaurus)
'bombed fort vanished' is the wordplay.
'bombed' is an anagram indicator.
'fort'+'vanished'='fortvanished'
'fortvanished' is an anagram of 'HAND OVER FIST'.
(Other definitions for hand over fist that I've seen before include "(Make, lose or spend money) very rapidly" , "(Gain) rapidly" , "With steady and rapid gain" , "In large amounts and swiftly" , "Rapid rate of money-making" .)