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Rocket Dreaming

By Richard P. Hallion
4/23/2018 • World War II Magazine

Ill-fated efforts to build rocket-powered fighters gave wartime aviation visionaries a humbling lesson in going nowhere fast.

On the early afternoon of May 29, 1944, Flight Lt. G. R. Crakanthorp rolled his Spitfire Mk XI reconnaissance fighter into a left bank, turning northwest high over Nazi Germany. At 37,000 feet, flying one of the fastest airplanes in the world, Crakanthorp had little to fear, but he was far

from complacent. Just a month earlier, British air intelligence had warned of a new Nazi weapon: a “strikingly unconventional” arrowhead design it called “the mystery plane of the war.” The intelligence report noted that all available evidence suggested the aircraft was rocket-propelled and concluded, “Its performance will undoubtedly be startling.”

So when Crakanthorp saw a rapidly approaching vapor trail angling toward him from the southeast, he prudently climbed. As his Spitfire reached 41,000 feet—near the limit of its supercharged Merlin engine—the pilot watched the trail come closer, pulsing in four short bursts. It closed rapidly to within a thousand yards, enough for him to discern a tiny sweptwing airplane at its apex. Then it dropped from sight.

The mystery plane turned out to be a rocket-propelled Messerschmitt Me 163 Komet, and Crakanthorp had the dubious distinction of being the first Allied airman to spot the German fighter as it raced toward him at an almost unbelievable speed. In an era when most airplanes flew at less than 300 mph, the Komet flew twice as fast thanks to its rocket engine, something up to then considered the stuff of black-powder fireworks and science fiction.

Unlike a piston- or gas-turbine-powered engine (more commonly known as a jet), both of which used air taken from the atmosphere, a rocket engine relied on a liquid oxidizer. The engine was simply a combustion chamber and nozzle in which fuel and oxidizer mixed and ignited. Since both the fuel and the oxidizer burned, the rocket’s total weight decreased rapidly while its thrust remained constant. This allowed it to accelerate ever faster until its propellants ran out, giving it unprecedented speed.

While enthusiasts seized on the rocket’s potential to fly into space or to other worlds, military rocketeers saw something else: a vision of invincible weapons; of missiles that could strike over hundreds, perhaps thousands, of miles; of rocket interceptors that could race aloft and shoot down far slower airplanes. A military equipped with rockets would be able to project its force higher, farther, and faster than one without them.

During the 1930s, the pervasive fear of aerial bombing had accelerated interest in the development of fast-climbing, highspeed interceptors. As a consequence, in the years just before and during World War II, Germany, Japan, the United States, and Russia all experimented with rocket-powered fighters. But while the technology had obvious appeal, these nations promptly discovered that it had an even greater downside. Even Germany’s fast, flashy Komet, the only rocket-powered aircraft to see combat during the war, proved a disappointment—noteworthy more for what its makers aspired to than for what they actually achieved.

This vision of indomitable power had particular appeal for Nazi Germany, which was locked in a struggle to the death against many foes. And the Germans were well positioned to lay its groundwork; since the 1890s, a powerful nexus of well-funded academic research centers, government and military laboratories, industrial research organizations, and superb educational facilities had produced a climate that ensured German scientific and technological excellence. During the interwar years, Germany pioneered advanced aerodynamic theory, long-distance sailplanes, all-metal monoplane airliners, gas turbine propulsion, and streamlined design. But rocketry was a particular fascination.

The Romanian German theorist Hermann Oberth forecast a future filled with rocket-propelled missiles and spaceships; civil engineer Walter Hohmann defined the orbital mechanics and transfer processes now critical to satellites and space probes. Popularists sketched rocket ships and rocket-propelled airplanes; some flew rocket-powered models, and a few actually constructed rocket cars and airplanes. Speed wasn’t the rocket’s only attractive trait: German army artillery officers realized that rockets could be used to circumvent the limits on cannon size and range imposed by the Treaty of Versailles, since the treaty did not specifically prohibit them.

Germany had also been prohibited from pursuing powered aviation in the years immediately after the Great War; as a means of maintaining aeronautical proficiency, it had turned to soaring. One of the greatest soaring designers was the pioneering aerodynamicist Alexander Lippisch, a believer in the Nurflügel—the pure flying wing. He built approximately 15 of them, including many variations, which he tested from a high plateau in the Rhön Mountains.

In 1928, automobile manufacturer Fritz von Opel, a flamboyant showman with a penchant for attention-getting stunts—including three demonstrations of rocket-powered cars—approached Lippisch about modifying one of his designs to demonstrate how the rocket might be applied to airplane designs. From this came the first flight of a rocket airplane, on June 11, 1928. That day, Fritz Stamer took off in a cloud of dense white smoke, his glider-turned-rocket-plane banking and turning over the plateau. Although Lippisch and Opel later had a falling-out, Lippisch focused on high-speed flight from that time on. In the drag-reducing benefits of a sweptback wing, combined with the power of jet and rocket engines, he saw the prospect of breaking the 1,000 km/h (621 mph) mark—and perhaps Mach 1, the speed of sound, as well.

German aircraft manufacturer Ernst Heinkel was pursuing the same goal. He realized that a piston-powered airplane could fly no faster than about 500 mph because of an unavoidable drop in propeller efficiency at that speed, and began searching for a power plant to, as he put it, “equal the speed of sound and perhaps to achieve supersonic speeds.” Heinkel’s passion led him to build an experimental rocket airplane, the He 176, which flew at Peenemünde-West in 1939. It was powered by a liquid-rocket engine, designed by propulsion engineer Hellmuth Walter, that burned a fuel called T-Stoff (80 percent concentrated hydrogen peroxide) mixed with Z-Stoff (potassium permanganate), generating an intensely hot, high-pressure oxygenated steam jet.

The He 176’s dramatic hissing roar and speedy climb was a good metaphor for the Wagnerian irrationality afflicting the Nazi state. A demonstration for Hitler on July 3, 1939, resulted in the führer awarding pilot Erich Warsitz 20,000 Reichsmarks. It was money well earned, for the He 176’s temperamental Walter engine had, at one point, abruptly quit; fortunately for Warsitz, he managed an immediate restart and narrowly avoided what almost certainly would have been a fatal crash. Testing ended that November, after just 48 flights.

Nonetheless, Heinkel’s work encouraged the Luftwaffe’s rocket ambitions, although his firm did not benefit from them. The nod had already gone—in early 1939—to his highspeed rival, the more politically astute Willy Messerschmitt. Previously, Messerschmitt had successfully courted Reich Air Ministry officials to gain their support for producing his Bf 109 fighter, even though it was inferior to Heinkel’s faster and more technologically advanced He 112; now he received air ministry approval to go ahead with a rocket fighter. He teamed with Alexander Lippisch, the start of an infelicitous partnership for both, as they clashed repeatedly. Nevertheless, out of that tempestuous relationship sprang the Komet.

By mid-1941, Messerschmitt had completed the first Me 163A, influenced by a design Lippisch had pioneered in 1937. The aircraft, made of mixed wood and metal and powered by a Hellmuth Walter–designed engine, first flew at Peenemünde on August 13, in the able hands of pilot Heini Dittmar. Slightly over six weeks later—on October 2, 1941—Dittmar became the first pilot to exceed 1,000 km/h, reaching 624 mph, although he nearly lost his life in the process. The sweptwing fighter had abruptly pitched downward at peak velocity just before exhausting its propellants, and was saved from breakup only by its exceptionally rugged structure. It was an ominous sign: as would prove true of almost all sweptwing tailless aircraft in the pre-computer-controlled era, the Komet was dangerously unstable as it neared the speed of sound.

Transforming the Me 163A into an operational fighter consumed the next two years. The result, the beefier Me 163B, had an armament of two 30mm Mk 108 cannons buried in its wing roots and employed a more powerful variable-thrust Walter engine, which used a cleaner-burning and therefore safer fuel. Messerschmitt and Klemm, a second-source contractor, built roughly 300 of the fighters. Following development trials with an elite corps of Luftwaffe test pilots, engineers, and maintenance personnel, known as Test Command 16, the Luftwaffe established a Komet fighter wing and, in the late spring of 1944, took the Me 163B to war.

While its performance was flashy, the Komet was hardly a great practical success. Launched against Allied bombers, the Komet had a phenomenal climb rate, reaching over 30,000 feet in approximately two and a half minutes. Yet that speed also hindered its effectiveness. At best, a Komet pilot could secure only one or two hits before overtaking his far slower target. Then, no matter how carefully he husbanded the plane’s fuel, the Komet would deplete it quickly; its power plant could run only four to six minutes at most with the 2,000 kilograms of fuel it carried, after which it would have to glide back to base, vulnerable to Allied fighters.

Over nine months of sporadic combat, Komet pilots claimed only nine definite and two probable aerial victories. Fourteen Komet pilots died in combat, and another 16 perished in accidents, bringing total fatalities to 30—nearly 12 percent of the entire Komet force. To be fair, this is far better than lurid postwar accounts of the fighter have suggested. Indeed, the Me 163 had proportionally fewer landing accidents than the tricky, propeller-driven Bf 109—the Luftwaffe’s most widely used fighter.

Nonetheless, the Luftwaffe quickly concluded that the Komet was not a useful warplane. One technical report from early 1945 concludes, “Experience with the Me 163 shows that expense and effort in materials, man-hours and pilot training are too high. The armament is insufficient for attack on bomber formations. The long airstrips are hard to camouflage. While gliding towards landing the aircraft are shot down by escort fighters.”

The Komet did, briefly, find another key group of admirers— in Japan. In late 1943, as the war began to turn against Japan and it anticipated the need for an interceptor, it contracted with Messerschmitt to build a derivation, the Mitsubishi J8M1 Shusui (“Slashing Sword”), and established a special interceptor unit, the 312th Naval Flying Corps, at Yokosuka. But the aircraft never saw combat. Mitsubishi completed only one powered J8M1, and on July 7, 1945, it crashed from engine failure on its only flight, fatally injuring its pilot.

After the war, Capt. Eric Brown, a highly experienced British pilot sent to Germany to assess its technology, observed a Walter engine test and called it “a frightening display, weird and futuristic.” He flew an Me 163A as well, finding the Komet “exhilarating” and its climb like “a runaway train,” though he still judged it a generally deficient, freakish design.

Even so, it wasn’t the strangest such program Germany had in the works. One day in August 1944, engineer Erich Bachem looked skyward as hundreds of amerikanische Bomber roared with impunity over his Waldsee manufacturing plant. That defining moment gave rise to a weapon Bachem summarized as a “combination airplane, rocket, and projectile”—the Bachem Ba 349 Natter. Pointed vertically on its launch rail, the tiny Natter—less than 19 feet long and spanning just 10.5 feet, with short wings, big tail surfaces, a rocket exhaust nozzle, and a small cockpit faired into the nose—looked exactly like what it was: a veritable piloted surface-to-air missile.

The Natter never enjoyed the enthusiastic support from the Luftwaffe that the Komet received, and for a while it seemed that the project might die. In desperation, Bachem appealed to an immensely powerful official, Heinrich Himmler. Himmler wore many hats: chief of the SS, overseer of the concentration camps, interior minister of the Reich, and chief of army armament procurement. Himmler was intrigued and granted Bachem an interview. The inventor left with Himmler’s strongest assurances of support, and the Natter project went ahead with a higher security priority than many of its more highly regarded rivals.

The aircraft wasn’t without merit: it was potentially more economical, less wasteful, and more easily manufactured than the Me 163, which was already reaping criticism for its shortcomings. Unlike the metal and wood Komet, the Natter was all wood except for some metal fittings, and designed to be launched vertically, off a guiding launch rail. That meant it received no lifting benefit from its wings during the early part of its ascent, and so had to depend entirely upon its rocket engine to climb into the air during the critical early seconds of flight. Though the Natter employed the same Walter engine used in later Komets, this power plant lacked the thrust necessary to accelerate it off the launch rail; therefore, detachable solidfuel rocket boosters were necessary to help kick it aloft.

The operational concept for the Natter was “one flight, one kill.” As an enemy bomber neared a Natter’s launch battery, the missile would roar up its launch rail, subjecting the pilot to more than two Gs of acceleration. After 12 seconds of flight, the solid-fuel boosters would detach and the Walter liquid-fuel sustainer engine would propel the Natter onward at about 435 mph. Once at altitude, the pilot would take control, level out approximately a mile behind the bomber stream, accelerate to more than 600 mph, select his target, jettison the nose cap to expose two dozen tube-launched 7.3cm Föhn explosive rockets, close to less than 300 feet, and then barrage-fire his rockets. Mission accomplished, he would glide earthward, slow down, jettison the entire nose section, and then drop out and parachute to earth. The Natter’s remains would descend to earth under a separate parachute, allowing its sophisticated Walter engine and even some of the airframe components to be salvaged, reassembled, and reused.

The Natter moved quickly from concept to flight test. On December 22, 1944, it was vertically fired for the first time to assess launch performance; it was also towed behind an He 111 to test basic airworthiness. Both tests were unpiloted. In late February, Hans Zübert, a highly experienced test pilot, flew the Natter as a glider after it had been carried aloft by a Heinkel. He dived the Natter at high speed, maneuvered, and bailed out. On February 25, Bachem conducted another unmanned test, launching a fully equipped Natter and recovering both the mannequin and rocket engine via parachute.

Encouraged, the SS proceeded to its first manned firing. On February 28, Oberleutnant Lothar Siebert, an enthusiastic volunteer, strapped himself into the little piloted missile and roared aloft. At approximately 300 feet, however, the cockpit cover unexpectedly flew off; the missile pitched on its back, climbed shallowly to about 1,800 feet, then dived into the ground and exploded. Whether Siebert was trying to bail out is unclear, but the Natter had claimed what would turn out to be its only victim.

The program went on to complete an extensive series of manned and unmanned test flights and demonstrations, and Bachem built approximately 30 Natters, launching 18 unmanned, one manned, and flying another as a manned glider. But none saw combat—both because the opportunity never presented itself, and because the Allies swiftly overran the production sites.

Additional time would have had little effect on the outcome, however. The Natter was simply an unworkable idea: it had little real military potential, required quantities of dangerous, exotic fuels and other substances, and would have required a huge support force of pilots and mechanics to keep it going. At the war’s end, six Natters were burned to prevent the Allies from seizing them; only four others survived. Intelligence personnel reported that some workers volunteered to build additional Natters for the Allies “in two or three months if given facilities for working.” It was an offer the Allies quite wisely refused.

Rocket research in the United States and Russia never reached the level of intensity that Germany’s did, but both had experimental combat aircraft programs, and both had similar glimpses of promise and failure.

In the United States, designers were already laboring to catch up with Britain and Germany in turbojet propulsion; as intelligence information indicated growing German interest in rockets, American authorities became determined not to fall behind in this field of technology as well. In September 1942, visionary designer John K. Northrop proposed to the Army Air Forces’ Air Technical Service Command that it sponsor development of a rocket-powered fighter that could reach the speed of sound: a flying wing known as the Northrop N-14 and, later, as the XP-79.

As it evolved, this concept led to a series of flying wing gliders, which were tested at Muroc Dry Lake in California beginning on August 27, 1943. In late spring of 1944, Northrop modified the second of these gliders to incorporate a rocket engine that burned a mixture of red fuming nitric acid (RFNA) and aniline, and designated it the MX-324. On July 5, 1944, Northrop test pilot Harry Crosby was towed aloft in the MX-324, trailing behind a Lockheed P-38 fighter. After being cast loose at 15,000 feet, Crosby ignited the rocket engine, flew for 10 minutes, and landed, successfully completing the first flight of an American rocket-powered airplane.

Although Northrop subsequently completed the XP-79, it was as a twin-engine jet rather than a rocket. The aircraft had been built with a magnesium structure. If any RFNA were to spill on it, the plane—as air force engineer Ezra Kotcher recalled years later—would have “fizzed like a piece of zinc in hydrochloric acid.” Northrop engineers had planned to use special metal coatings to prevent such a disaster, but eventually they recognized the impracticality of the rocket design and choose to install two small Westinghouse jet engines instead. On the first flight of the jet version of the XP-79 on September 12, 1945, the aircraft went out of control, and Crosby was killed.

Rocketeers in Russia had an earlier start, drawing on the inspiration of Konstantin Tsiolkovsky, one of the great prophets of the space age, to create a Rocket Scientific Research Institute in 1934 to promote military rocketry. By mid-1937, its work had led to development of 82mm and 132mm rockets air-launched from Polikarpov I-16 fighters, the predecessors of modern airto-air missiles. In 1940—one year later than Nazi Germany— Russia flew a rocket-propelled testbed, the RP-318, derived from a sailplane designed by Sergei Korolev, who would eventually oversee the Sputnik program and the early Soviet-manned spacecraft program.

While otherwise unimpressive—it retained the slow and stately character of a glider, not the speed and drama of a Komet-like fighter—the RP-318 led to development of a rocket-propelled interceptor, the BI-1. Like the Komet, it featured mixed wood and metal construction, although its aerodynamic design was altogether better. The BI-1 was an attractive monoplane, with a retractable landing gear and twin 23mm cannons, powered by a rocket engine that burned kerosene and nitric acid.

On May 15, 1942, test pilot Grigori Bakhchivandzhe completed the aircraft’s first flight at Koltsova Airfield outside Sverdlovsk. Subsequent testing went surprisingly smoothly, but on March 27, 1943, disaster struck: the BI-1 broke up during a low-altitude high-speed run, killing Bakhchivandzhe. By this time, the Russo-German air war had changed; German bombers were no longer striking deep against Russian cities, and the Soviets were more in need of tactical fighter-bombers and attack airplanes to operate over the battlefield. Acquisition authorities decided the time had come to abandon the BI-1.

Just after World War II, Russian technologists experimented with a final rocket-powered fighter, which they envisioned as a means of countering American bombers armed with an atomic bomb. The MiG design bureau drew upon German work to make the I-270 in 1946. Although it entered flight testing, it too failed to enter service because the jet airplane was better suited for a variety of combat missions, not just up-and-down interception. Although some jetfighters later flew experimentally with small liquid-fuel rockets added to them for combat boost, and designers continued to draw up proposals for rocket fighters, the concept of the rocket-powered fighter effectively died away after the I-270.

In hindsight, the rocket-powered fighter was a dangerous and immature delusion. Conceived as a cheap means of furnishing protection against bomber attack, it had little offensive potential, and no real value after mid-1943 to either the United States or Russia. Although the concept may have seemed simple, it was very complex in reality, demanding highly specialized development, and requiring such a high standard of personnel that, even as a defensive system, it made little sense. It was a transitory vehicle, quickly supplanted by the genuine revolution embodied in the jet engine and high-speed aerodynamics, which led to the jetfighters of the cold war and afterward.

What the rocket fighter movement did generate, however, was faith that humanity could exceed the speed of sound, and perhaps indeed fly in rocket-powered aircraft into space. Both those expectations were fulfilled: first by the rocket-propelled Bell X-1, the world’s first supersonic airplane, and then by the hypersonic North American X-15 of the 1960s. In 1981, when the space shuttle Columbia rocketed into space, it fulfilled a dream of centuries, but, as well, a dream inherent in the work of the rocket fighter pioneers of World War II.


Originally published in the November 2008 issue of World War II Magazine. To subscribe, click here

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