I believe that a squadron was 12 operational pilots/aircraft but wasnt the strength 16 men and machines at the start to guarantee (as far as possible) that 12 were available. This is a sensible contigency for operations, quickly swallowed up when battle starts.When things got really tough the rotation of entire squadrons stopped. Fresh squadrons with inexperienced pilots simply took heavier losses than the squadrons they replaced. For example, No. 616 Squadron lost 5 pilots and 12 aircraft in a week (25th August - 2nd September).