Why did fleet air defence use about eighteen fighters rather than a simpler multiple of four?
Short answerThe figure supported layered long, short, and alert CAPs and enough rapid reinforcement to protect the force, particularly before airborne early warning.
NotesThe eighteen-fighter figure was not a relic of an early-war three-aircraft formation. Fleet defence used a long combat air patrol farther out, a short patrol nearer the force, and an alert group ready to launch. That layering mattered especially before airborne early warning could extend detection time. The number therefore reflected how many fighters could be kept in the air or brought up quickly enough to reinforce the cover. Falling below it increased the risk that one layer would be too weak when an attack arrived.