A drama about flotilla (6)
I believe the answer is:
armada
'flotilla' is the definition.
(I have seen 'Large flotilla' mean 'armada' so perhaps 'flotilla' could also mean 'armada')
'a drama about' is the wordplay.
'about' indicates anagramming the letters.
'drama' with letters rearranged gives 'rmada'.
'a'+'rmada'='ARMADA'
(Other definitions for armada that I've seen before include "The Spanish force" , "Large number of ships (Spanish?)" , "Large war fleet" , "A great fleet of warships" , "Spanish fleet sent in 1588 to escort an invasion of England" .)