fighter included endurance with drop tanks of two hours at full power, or six to eight hours at cruising speed. Drop tanks were commonly used with the Zero, even on combat air patrol (CAP). The Zero entered service in 1940.

American bomber theorists (the so-called Bomber Mafia) wanted to create self-defending fleets of heavy bombers. Consequently, American policy opposed drop tanks but airmen such as Benjamin S. Kelsey