In 1951, de Havilland debuted the D.H.112 Venom, evolved from the Vampire with a Ghost engine (again the ghoulish theme), which was 40 percent more powerful than the Goblin. By 1960, when this Addams family of twin-boom jets culminated with the all-weather, swept-wing D.H.110 Mk. 2 Sea Vixen, the booms were called on to do more than support the tail assembly. Packed with tanks, they were extended forward of the wings to carry more fuel for the two 10,000-pound-thrust Rolls-Royce engines.
Called “the fork-tailed devil” by the Germans, the Lockheed P-38 Lightning was also called “funny-looking” by the U.S. Army when its representatives saw the design in early 1937. Lockheed designer Kelly Johnson famously wrote in his autobiography that by the time the Lockheed team had stuffed the long Allison inline engines into nacelles with turbo-superchargers and landing gear, “we were almost back to where the tail should be. So, we faired it back another five feet….” Johnson needed two 1,150-horsepower Allison V-1710 engines to achieve the required speed of 360 mph (the operational fighter bested 400) and climb rate of 20,000 feet in six minutes. The design enabled him to cram in all that propulsion with the smallest drag penalty. The centerline cockpit nacelle allowed for good visibility and carried four machine guns and a cannon—a devastating stream of forward fire without the complication and weight penalty of an interrupter gear to keep the guns from shooting a propeller blade.
Although the P-38 is the most famous twin-boom combat aircraft of World War II, it is not the first. That distinction belongs to the Fokker G.1, which first flew in 1937, two years before the XP-38.
A distinguishing feature of the other U.S. twin-boom fighter to enter service during the war, Northrop’s P-61 Black Widow, was the big radar in its nose, which enabled it to fly missions at night. It carried up to three crewmen in the central fuselage, four belly-mounted 20-mm cannon firing forward and, in some models, a powered, remote-controlled turret equipped with four .50-caliber machine guns. Gerald H. Balzer, a former Northrop engineer, says the design team worked from a sketch made in 1940 by the Air Technical Service Command at Wright Field in Ohio. His thoughts on the twin-boom arrangement: “The configuration of an airplane depends on what you want to cram into it.”
Giulio Douhet and Gianni Caproni could be considered the twin pillars of Italian air power in World War I. Because of their collaboration, says historian John H. Morrow Jr. of the University of Georgia, “Italy put up a very strong aerial effort in relationship to its economic resources.”
Morrow adds: “Douhet believed that you could knock another country out of the war by bombing strategic targets—hydroelectric plants, railway stations and junctions, ammunition stockpiles, and factories. And Caproni was willing to design large aircraft to do just that.”
With a wingspan of 73 feet, Caproni’s Ca.3 biplane bomber was one of the largest aircraft fielded in World War I, almost 20 feet wider in span than the war’s other twin-boom biplane bomber, France’s Caudron G.4. (It was a big-airplane war: Handley Page built a four-engine giant with a 120-foot wingspan.)
Like so many of its contemporaries, the Caproni bomber used a combination of pusher and tractor propellers; Caproni placed the pusher at the rear of a short, bathtub-like fuselage, the only ungraceful feature of a beautifully proportioned airplane. Its most famous missions were low-level night raids, flown in 1917 across the Adriatic Sea, to surprise the Austro-Hungarian fleet while it was at anchor in Pola (today Pula), Croatia.
The year before, a second gunner’s position was added above the rear engine. “It must have been a ferociously difficult position,” says Morrow, the author of The Great War in the Air (Smithsonian Institution Press, 1993). “It was located up and in the slipstream and the weather. Many of those crews won Italy’s highest honor for bravery in combat. I marvel at what men did in World War I.”