A combat air patrol's first purpose was to break up an incoming strike so the carrier did not face a coordinated attack from several directions. Heavy anti-aircraft fire could divide the formation further, leaving medium weapons to engage smaller groups or individual aircraft. Light weapons also served as a close warning to the ship. Maintaining four fighters on station called for more than those four aircraft: another four waited on deck alert, with further groups available in the hangar and two spares bringing the suggested total to eighteen. As the patrol intercepted, the alert group launched and the next group moved up. The rotation protected the carrier against successive waves while returning fighters refuelled and rearmed.
Notable Point · 28:49-31:08
Why an eighteen-fighter force supported a four-aircraft patrol
The eighteen-fighter example explains the aircraft needed behind each patrol and why disrupting an attack mattered as much as shooting down aircraft.