Bomber Harris finally left low barracks (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

An envelope (‘barracks’) of S (‘Harri S finally’) plus QUIT (‘left’) in MOO (‘low’). The de Havilland Mosquito was a World War II warplane, and Bomber Harris, Marshall of the RAF, was CinC at the height of the bombing campaign.