Red butterfly in charge of the fleet? (7)
I believe the answer is:
admiral
'red butterfly in charge of the fleet?' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for admiral that I've seen before include "Top-ranking naval officer" , "Highest ranking naval officer" , "Naval high-up" , "Red butterfly at sea?" , "[NELSON] perhaps" .)