Lockheed P-38 Lightning
The Lockheed P-38 Lightning was a World War II American fighter aircraft built by Lockheed. Developed to a United States Army Air Corps requirement, the P-38 had distinctive twin booms and a single, central nacelle containing the cockpit and armament. Named "fork-tailed devil" (der Gabelschwanz-Teufel) by the Luftwaffe, the P-38 was used in a number of roles, including dive bombing, level bombing, ground-attack, night fighting, photoreconnaissance missions, and extensively as a long-range escort fighter when equipped with drop tanks under its wings.
The Lockheed design team, under the direction of Hall Hibbard and Clarence "Kelly" Johnson, considered a range of twin-engine configurations including both engines in a central fuselage with push-pull propellers.
The eventual configuration was rare in terms of contemporary fighter aircraft design, with only the preceding Fokker G.1, contemporary Focke-Wulf Fw 189 Luftwaffe reconnaissance aircraft, and the later USAAF's Northrop P-61 Black Widow night fighter having a similar planform. The Lockheed team chose twin booms to accommodate the tail assembly, engines, and turbo-superchargers, with a central nacelle for the pilot and armament. The XP-38 gondola mock-up was designed to mount two .50 caliber (12.7 mm) M2 Browning machine guns, with 200 rpg, two .30 caliber (7.62 mm) Brownings, with 500 rpg, and a T1 Army Ordnance 23 mm (.90 in) autocannon with a rotary magazine as a substitute for the non-existent 25 mm Hotchkiss aircraft autocannon specified by Kelsey and Saville. In the YP-38s, a larger John Browning-designed, Colt-made M9 37 mm (1.46 in) autocannon with 15 rounds replaced the T1. The 15 rounds were in three 5-round clips, an unsatisfactory arrangement according to Kelsey, and the M9 did not perform reliably in flight. Further armament experiments from March to June 1941 resulted in the P-38E combat configuration of four M2 Browning machine guns, and one Hispano 20 mm (.79 in) autocannon with 150 rounds.
Clustering all the armament in the nose was unlike most other U.S. aircraft which used wing-mounted guns with trajectories set up to crisscross at one or more points in a convergence zone. Guns mounted in the nose did not suffer from having their useful ranges limited by pattern convergence, meaning good pilots could shoot much farther. A Lightning could reliably hit targets at any range up to 1,000 yd (910 m), whereas other fighters had to pick a single convergence range between 100 and 250 yd (230 m). The clustered weapons had a "buzz saw" effect on any target at the receiving end, making the aircraft effective for strafing as well. The rate of fire on the guns was about 650 rounds per minute for the 20×110 mm cannon round (130 gram shell) at a muzzle velocity of about 2,887 ft/s (880 m/s), and for the .50 caliber machine guns (43–48 gram rounds), about 850 rpm at 2,756 ft/s (840 m/s) velocity. Combined rate of fire was over 4,000 rpm with roughly every sixth projectile a 20 mm shell. The duration of sustained firing for the 20 mm cannon and .50 caliber machine guns was approximately 14 seconds and 35 seconds, respectively.