In May 1945, a Soviet intelligence official picking his way through the ruins of the Peenemünde rocket complex on the Baltic coast decided to relieve himself behind a woodpile. Whilst in the act, he stumbled across a secret document about a spaceplane, one that would eventually lead to the botched kidnapping of a German engineer in France four years later, and an abortive Russian attempt to build a spaceplane capable of delivering a large bomb to the heart of New York.
What made Josef Stalin send his own son, a Russian rocket scientist, and a team of kidnappers to Paris to snatch a rocket engineer and his mathematician wife away from possible American influence? The answer lies in a 1930s spaceplane project that is still largely unknown and unrecognized today: Silbervogel.
Everyone knows Germany was way ahead of its time when it came to dreaming up radical weapons systems during World War Two. Superguns and vertical take-off rocket planes have already had their stories told in The Debrief. However, what would have been termed an Amerikabomber during the conflict had already been conceived and designed well before the outbreak of war in September 1939. It was something that would be regarded as a spaceplane today. This amazing design was known as the Silbervogel (“Silver Bird”), and its genesis lay in an engineering student’s thesis back in 1931.
Skimming Stones and Rocket Sleds
At the age of just 26, Eugen Sänger came up with the idea of a rocket-powered sub-orbital craft and entered it as his thesis for the Vienna Polytechnic Institute. However, this was deemed too radical for 1931 and was summarily rejected, forcing the prospective engineer to submit a much more acceptable proposal. Not one to be disheartened, Sänger arranged for his original idea to be published as a book titled Raketenflugtechnik (“Rocket Flight Engineering”) two years later. He also sent a 16-page proposal to the Austrian Ministry of Defense, which contained the following observation:
“Both the speed of customary aircraft and the operational altitude have now approached limits which, as far as can be foreseen, will not be extended significantly by the means now in use.”
The young engineer clearly had much more radical technology in mind. At the same time, he worked on designing a regeneratively-cooled rocket motor that would prevent the engine from overheating. Sänger eventually came up with the idea of circulating rocket fuel around the exhaust nozzles before burning it in the engine itself – a practice which can still be found in today’s motors. The patent for this was filed in 1935.
That same year, he published an article in the Austrian journal Flug (“Flight”). This, together with his book, attracted the attention of the Luftwaffe. Two years prior to the 1938 Anschluss, he was invited by the Reichsluftministerium (RLM, or “State Air Ministry”) to establish a small research facility within the Reich. Sänger began work on his Silbervogel concept at the new institute located near Braunschweig. The Germans also constructed a liquid oxygen plant at the facility, plus a test stand for a 100-tonne thrust rocket engine, confirmation of their great interest in the engineer’s ideas. Rocket rivalry was alive and kicking in 1930s Germany; the Austrian upstart’s work did not sit well with Wernher von Braun, who may have believed that the Austrian’s work rivaled his own. However, attempts to curtail or cancel Sänger’s project came to nothing. The engineer also hired an assistant, a young engineer, mathematician, and physicist named Irene Bredt, who would end up working alongside him for the next twenty years. The two were married in 1954.
Silbervogel comprised what would later be described as a lifting body. It featured a fuselage of flat, rectangular design, measuring 91 feet 10 inches long, 9 feet 11 inches wide, and 6 feet 11 inches deep. The pointed forward fuselage opened out in sections towards the mid-point where two comparatively short wings were fitted. These had a span of just 49 feet across. The rear fuselage tapered slightly inwards, reaching a blunt tail edge from which protruded the primary rocket engine nozzle, which was flanked by two auxiliary rockets. A small horizontal tailplane carried even smaller endplate tailfins.
Although Sänger envisaged Silbervogel landing on a conventional runway, and therefore included a retractable undercarriage in his design, the take-off procedure he had planned was completely radical. Science-fiction fans who remember the spaceplane’s take-off in the 1951 movie When Worlds Collide will have a head-start here. Ignoring its tall tail fin, the movie’s craft seemed to closely resemble the German design. Sänger proposed that Silbervogel was to take off from a streamlined rocket-powered sled that sat on a monorail track measuring 1.8 miles (3 km) in length. If that was not impressive enough, the rocket motor designed for the sled itself was to generate some 600 tonnes of thrust for 11 seconds, over three-quarters of that generated by the eight H-1 engines fitted to the S-I first-stage launcher of the Saturn I.
Once detached from the sled and airborne using its auxiliary engines, Silbervogel would fire up its main 600 tonne-thrust rocket motor at an altitude of 5,000 feet, which after burning for eight minutes would propel the craft to an altitude of 90 miles and a speed of 13,730 mph, or Mach 17.89. To reach distant targets – say the eastern coast of the United States – an equally impressive procedure would be carried out. After the main rocket engine burned out, Silbervogel was supposed to descend at high speed towards the thicker atmosphere layers and then “skip” back upwards, like a flat stone skimming over the water. This would be repeated until the craft ran out of momentum due to drag, at which point it would glide down towards a conventional landing on a runway, presumably a very long one. The projected distance for such a flight was calculated at around 14,600 miles. Problems with airframe heating were predicted but Sänger believed that the upward flight from each “skip” would allow the craft’s surface to cool down to within acceptable limits. Three months before the start of World War Two, Sänger embarked upon a series of friction tests and had also begun construction on a 1/20th scale model of Silbervogel.
A Good Old Fashioned Math Problem
With the outbreak of war, Sänger was forced to either abandon his project and concentrate on more conventional rocket-powered aircraft research or adapt Silbervogel for military purposes. He chose the latter, and the spaceplane suddenly became a possible method of striking America, should it ever enter the war. An Amerikabomber was therefore a reality – at least in terms of a working project – at least two years before the United States was at war with Germany. Sänger and Bredt developed the plan together, turning it into a weapon that had enough range to reach the eastern seaboard of the United States. Once there, it would drop an 8,800 lb bomb on a target and then continue flying over the continent and the Pacific Ocean, landing somewhere within Japanese-held territory. Such a flight was calculated by the two engineers as being between 12,000 and 15,000 miles, which was within the theorized capabilities for Silbervogel.
Sänger’s work on the 100-tonne main rocket motor proceeded up until 1941 and showed some early promise, even apparently outshining the progress made across at Peenemünde on the engines for the V-2 missile. But these were early days and V-weapons research enjoyed a much greater priority in the Reich, not least due to its support by senior figures across the Reich. In 1942, the RLM suddenly ordered Sänger to cease all work on his rocket engine. The engineer was transferred to the Deutsche Forschunganstalt für Segelflug (DFS, or “German Gliding Research Institute”), where he worked on ramjet-powered aircraft designs until the end of hostilities. It is probably just as well that Sänger’s project never got to the point where one was actually test-flown across the Atlantic. Post-war experts analyzed the computations that he and Irene Bredt had used to work out the heat flow during re-entry. They found a mathematical error, one which showed that the levels would have been far greater than the Austrian engineer had allowed for in his design. Using these flawed calculations, such a craft – and its unfortunate pilot – would have burned up during this phase of the mission.
However, all of this was unknown to Sänger and Bredt in 1944 when they were able to submit a revised proposal to the RLM for two separate Silbervogel variants. The shorter-range Antipodenferngleiter (“antipodal long-range glider”) was designed with a New York bombing raid in mind, whilst the Interglobalferngleiter (“intercontinental long-range glider”) design would have allowed Sänger’s spaceplane to theoretically attack any target, anywhere in the world. 100 copies were distributed among various influential officials and agencies across the Reich. It was one of these that the Russian official stumbled across whilst taking a piss at Peenemünde.
Silbervogel was, however, way ahead of its time. Without competing projects for money, materials, and testing facilities, such a project could theoretically have been built in Nazi Germany, as senior Party members were certainly fond of grandiose schemes. If heat-resistant ceramics had been available for the spaceplane’s undersides, then it may not have even burned up on re-entry, despite the flaws in the mathematics. However, Silbervogel was a long-term project, not something that could simply be put together in a matter of a few years and thrown into combat. If the Germans had thrown money and resources at the project, and the war had not intervened, then such a craft may have been ready about 1955 or so – when in reality the Russians might have decided to build one themselves, if it had not been for the advent of ICBMs.
Cruise Missiles, Dyno-Soars and Robotic Spacecraft
The secret document on Silbervogel found its way to Josef Stalin’s desk in Moscow. He was suitably intrigued by the nature of the planned weapon, and in November 1946 ordered the establishment of an Opytnoye Konstruktorskoye Byuro (OKB, or “Experimental Design Bureau”) devoted to studying the concept. Mstislav Keldysh, a Latvian mathematician and engineer, was placed in charge of this new OKB and set to work studying the Silbervogel documentation.
Keldysh eventually redesigned the orbital bomber concept by using ramjets instead of rocket motors in order to save weight, but the work proceeded incredibly slowly. Stalin was informed that a draft project would not be available for five years, possibly more. By the time the OKB was ready, the plan had been overtaken by progress in missile development. The introduction of intercontinental ballistic missiles rendered Sänger’s concept obsolete and the Keldysh version of the Silbervogel was canceled. This work was not in vain, however; it led to a whole series of studies for Soviet ramjet-powered cruise missiles in the 1950s, although all of these were eventually canceled too.
The Boeing X-20 Dyno-Soar owes a lot to the Silbervogel project. Walter Dornberger and Krafft Ehricke had been involved in the German V-2 program and began working for Bell Aircraft after the war. Both had knowledge of Sänger’s wartime project, and in 1952 proposed an American version which was called the “Bomber Missile.” Attempts to recruit Eugen Sänger to the project ended in failure, but it went ahead anyway, eventually evolving into three separate proposals, meeting requirements for sub-orbital research, reconnaissance, and bombing platforms. The projects were soon transformed into the X-20, with seven astronauts being chosen for flight trials. However, problems regarding which type of booster rocket to be used and a lack of direction in terms of project goals meant that a decision was taken to go with the Gemini rocket program instead, and Dyno-Soar was finally scrapped in December 1963.
The spaceplane concept did not die out with the Dyno-Soar though. Boeing resurrected the concept with their X-37 proposal in 1999, the spaceplane eventually becoming a reality in April 2010 with the launch of Orbital Test Vehicle 1 (OTV-1). The unmanned craft spent nearly seven and a half months in orbit. Another five launches (that are known about) were carried out between March 2011 and May 2020, the last being OTV-6, the first X-37B launch by the United States Space Force. This spaceplane is still in orbit today. The Chinese have their own similar craft, known as the Shenlong program, whilst a whole host of nations have at some stage toyed with the idea of creating their own spaceplanes.
The Russian Botched Kidnap Attempt
Back in the immediate post-war period, Stalin clearly expected to see results, and quickly. America already had the atom bomb, and he wanted an effective delivery system for the Soviet Union’s own bomb program which was underway. It was not guaranteed that Russian bombers could survive long enough to reach American cities, but this German spaceplane idea could. Stalin seized upon the idea of bringing Sänger to the Soviet Union to work at the Keldysh OKB, but how was this to be arranged? The German, together with his assistant, Irene Bredt, was understood to be living in the Western Zone. It would have been an easy matter to spirit them away in the dead of night if they had been living in the Eastern Zone; after all, some 6,000 designers, engineers, scientists, and their families had been moved to Russia from the Soviet Zone of Occupation on 22nd October 1946 in an operation known as Osoaviakhim, a one-night effort rivaling the American Paperclip brain-drain. Snatching them from under the Americans’ noses meant that something more drastic was needed.
Eugen Sänger and Irene Bredt somehow got wind of the Soviet interest in their wartime work. They had managed to evade American attempts to recruit them but given the possibility that the Russians might try to coerce them into traveling to the Eastern Zone where they would be at the mercy of Stalin’s henchmen, they accepted a French offer to work on ramjets and rocket propulsion technology. Meanwhile, Stalin instructed his own son, Vasily, and the rocket scientist Grigori Tokaty to find Sänger. Their orders were to convince the Austrian engineer to come to the Soviet Union. Conscious of possible failure by his son, Stalin also ordered a team of secret policemen to accompany the effort, their orders being to kidnap the German couple if negotiations failed. Sänger and Bredt were now in Paris, working for the French government, and would go on to found the Fédération Astronautique. It is believed that intelligence officers tipped Sänger and Bredt off about the potential of a Russian kidnap attempt.
Vasily Stalin and Grigori Tokaty were clumsy in their efforts to persuade the German engineer to work in Russia. They first traveled to Berlin, then to Vienna, and then to various other locations across Europe before finding out that the German couple were actually in Paris. They tried contacting them there but were rebuffed each time. The planned kidnap attempt by the Soviet secret police team was also botched because a Soviet aircraft engineer named Tokayev, who had knowledge of the operation, defected to Britain and blew the whistle on their plans. The Russian engineer even went as far as to have an article on the planned kidnap published in the British Daily Express newspaper. French secret police thwarted subsequent attempts to remove the German couple. The Russian snatch squad was forced to leave France empty-handed, and Silbervogel never flew with a red star painted on it.
Follow and connect with author Graeme Rendall on Twitter: @Borders750