Why eighteen aircraft became a carrier minimum

Royal Navy exercises under Rear Admiral Henderson around 1931-32 identified eighteen fighters as the minimum for sustaining combat air patrol through repeated raids. The arithmetic quickly uses four groups of four: one engaging the enemy, one moving into patrol position, one on deck alert, and one returning or being serviced. Two spare airframes cover maintenance and serviceability losses. Eighteen is a floor, since a large raid can require extra fighters and consume the margin. The same rotation problem applies to helicopters hunting submarines. A proposed Queen Elizabeth-class air group combines eighteen F-35B fighters with eighteen Merlins, or more helicopters including airborne early warning versions. Modern fighters can fire missiles before closing with an attacker, but must still return for checks, fuel, and ammunition. Alert fighters and aircraft brought up from the hangar keep the cycle moving while the returning patrol is serviced.