Before dawn on June 22, 1941, German bombers began to rain destruction down on a swath of Soviet cities from Leningrad to Sevastopol. It was the beginning of Operation Barbarossa, the largest military operation in the history of the world. By the end of the day, three million German soldiers and their allies crossed the Soviet border, inaugurating the bloodiest phase of World War II. The invasion also brought to a bloody conclusion 20 years of secret cooperation between Germany and the Soviet Union.

While Soviet-German military cooperation between 1922 and 1933 is often forgotten, it had a decisive impact on the origins and outbreak of World War II. Germany rebuilt its shattered military at four secret bases hidden in Russia. In exchange, the Reichswehr sent men to teach and train the young Soviet officer corps. However, the most important aspect of Soviet-German cooperation was its technological component. Together, the two states built a network of laboratories, workshops, and testing grounds in which they developed what became the major weapons systems of World War II. Without the technical results of this cooperation, Hitler would have been unable to launch his wars of conquest.

After World War I, the victors dismantled the vaunted German army, reducing it to only 100,000 men. The Treaty of Versailles further forbade Germany from producing or purchasing aircraft, armored vehicles, and submarines. These provisions highlighted the Entente’s hope that removing German access to modern technologies of war would force Germany to abandon its militarist past. To the contrary, those particular provisions further convinced the remnants of the German High Command that technological rearmament was essential to restoring Germany’s position. Few works since the opening of the Russian Archives have explored the Soviet-German military pact in its totality. None have focused on its technological aspects. In this article, I offer new conclusions on the subject, drawing from archives in Russia, Germany, the United Kingdom, Poland, and the United States. Of particular importance for this piece are the Russian State Military Archive (RGVA), the archives of the German corporations Krupp, M.A.N. and Daimler-Benz, the U.S. National Archive’s Collection of Foreign Records Seized, and Yale University’s Russian Archive Project.

General Hans von Seeckt, in command of the Reichswehr from 1920 to 1926, was eager to work with Soviet Russia, the only other European state equally hostile to the status quo. In 1919, Seeckt dispatched to Russia Enver Pasha, the former Turkish minister of defense then in hiding for his part in mass atrocities against Armenians in eastern Anatolia. Seeckt’s goal was to establish communications with the Soviet government to discuss the possibility of military cooperation. He was particularly eager to work against the newly revived state of Poland. German military leaders saw it as the “pillar of Versailles” — a French puppet designed to encircle Germany from the east. Its absorption of former German territory that included hundreds of thousands of ethnic Germans further inflamed Berlin’s hostility.

Enver’s first mission ended disastrously when his plane crash-landed in Lithuania and he was detained by the new Lithuanian government. He was carrying sensitive materials from the German military that might have ignited calls in Great Britain and France for the occupation of Germany. Only a daring jailbreak by a junior German officer prevented Enver and the secret documents from falling into Allied hands. But the following year, he made the attempt again and succeeded. The Enver wrote back to Berlin that

Today I spoke with … Trotsky. With him there’s a faction that has real power, and also includes that party that stands for an understanding with Germany. That party would be willing to acknowledge the old German borders of 1914.

That meant the extinction of Poland. This was exactly the hope of the German officer corps.

Leon Trotsky, then head of the Red Army, saw cooperation with Germany against Poland as a central pole in Soviet strategy. He wrote that “Poland can be a bridge between Germany and us, or a barrier.” After the Red Army’s defeat in the Polish-Bolshevik war, it had become a barrier. Bolshevik leadership believed in 1920 that only with access to the industrialized economies of the West could the Bolshevik revolutionary regime survive. As long as the state of Poland existed, this mutual objective proved to be a lodestar, guiding Berlin and Moscow in parallel.

At the Treaty of Rapallo in April 1922, Germany and the Soviet Union normalized relations for the first time, the first blow against the postwar order. The following summer, the Reichswehr and Red Army held a series of secret summits during which they crafted the framework for military cooperation. At first, Hans von Seeckt envisioned German military-industrial firms moving banned production and research to the Soviet Union. His staff earmarked considerable portions of the Reichswehr’s “black funds” — financial resources hidden from the German government — to subsidize these programs. To accommodate German firms, Lenin personally supervised the establishment of a concessionary system whereby German corporations could take over and modernize existing Soviet industrial plants under the close supervision of Soviet officials. Under the auspices of this program, German firms took over shipyards, factories for aviation, artillery, grenades, and rifles, chemical weapons plants, and other critical facilities. German businesses expected to profit from these ventures, but also hoped to find a new home for military experts, technical testing, and production in banned fields. Seeckt envisioned these factories one day supplying the reborn German army in a future war with France. The Soviets, in turn, hoped to increase their military industrial production cheaply, gain access to German technology, and train hundreds of new engineers.

Most of these ventures failed in the difficult economic circumstances of early Soviet Russia. The most important of these arrangements, a massive Junkers aircraft production facility outside of Moscow, failed to live up to either sides’ expectations, although it did become one of the most productive aircraft facilities in the Soviet Union. In December 1926, after massive financial losses, the owner of Junkers owner leaked details on the German program in Russia to members of the Reichstag, Germany’s parliament. On December 3, 1926, the scandal became public when a seven-line headline appeared in the Manchester Guardian, proclaiming: “Cargoes of Munitions from Russia to Germany! Secret Plan between Reichswehr Officers and Soviet[s]. STARTLING DISCLOSURES…” The German government, largely ignorant of ongoing Reichswehr efforts in the Soviet Union, fell in disgrace after a vote of no confidence in the Reichstag.

The scandal seemed to undo the grand hopes the German and Soviet militaries had invested in cooperation. But instead, the Soviet-German military relationship took on new life. Beginning in 1925 and growing rapidly after the Junkers scandal, the two militaries established a series of secret military bases at which German and Soviet officers lived, studied, and trained side-by-side. Teams of engineers and scientists worked on new weapons systems and reverse-engineered American, British, and French military equipment. Two of these bases were devoted to chemical weapons production, one to aviation training, and one to armored warfare. These bases helped to modernize the Red Army and played a central role in developing the military technologies that would enable the rebirth of the German military under Hitler .

The first cooperative base to open was a flight school located at Lipetsk, a city some 500 kilometers southeast of Moscow. Beginning in 1924, the Soviet Air Force invited German pilots to the Lipetsk Air Field to participate in flight training. A year later, the Soviet Air Force transferred the facility to the German military, although part of the agreement required the Germans to train Soviet officers and mechanics at the facility. In 1927, after the Junkers scandal, Lipetsk expanded massively in scope. Nearly 1,000 German pilots, observers, mechanics, and engineers would live at Lipetsk during its period of operation. They would become the core of the Luftwaffe when it reemerged in 1935. In addition, the Soviets and Germans sent many of their top test pilots to Lipetsk to fly their newest designs. All seven aircraft manufacturers in Germany secretly sent their prototypes — most of them violations of Versailles — to Lipetsk for testing. More important for the future were the intellectual exchanges that occurred there. The Germans borrowed Soviet concepts such as paratroopers and the dive bomber from the Red Air Force. The Red Air Force, in turn, learned tactical and operational lessons from German instructors, copied German designs, and — when unsatisfied with technical cooperation — stole design blueprints from their German partners.

As Lipetsk became operational, the Red Army and Reichswehr laid the foundations for an armored warfare and testing grounds located in the city of Kazan, 800 kilometers east of Moscow. Here, too, German and Soviet armored officers trained side-by-side. In addition, the major German corporations secretly involved in Germany’s illegal tank construction program — Krupp, Daimler, and M.A.N. — sent their engineering teams to Kazan. These engineers lived, worked, and tested new tank designs in Kazan that would lead to the Panzers I through IV, representing the majority of German tank production during the coming war. Soviet technical gains were also considerable: One Red Army officer wrote that the joint base at Kazan had resulted in the redesign of most of the Soviet Union’s armored vehicles. His report, preserved in the Russian State Military Archives, further noted that the Red Army had learned “a lot of interesting things on methods in tactics, the technique of driving vehicles, and marksmanship. Thus, in general, the work of TEKO [codename for the base] has been of great interest to the Red Army…” Further, the top theorists of warfare on each side — Heinz Guderian, Oswald Lutz and Ernst Volckheim for the Germans, Mikhail Tukhachevsky and Vladimir Triandafillov for the Soviets — visited, worked and in some instances taught as instructors in Kazan, training the next generation of armored warfare officers.

Starting in 1926, the two sides also began collaborating on chemical weapons development. At two facilities — Podosinki near Moscow, and Tomka near Samara — Soviet and German scientists experimented with new agents and dispersal techniques, as well as medical treatments for poison gas casualties. In addition, the German military helped Yakov Fishman, head of the Soviet chemical weapons program, hire German scientists and firms driven underground by the ban on chemical weapons. Both Germany and the Soviet Union profited from this illicit trade, which developed into a cornerstone of the Soviet-German relationship. By 1931, German scientists and engineers were managing about half of the Soviet Union’s vast chemical weapons production program. Critically, technical experiments in Russia convinced Reichswehr leaders that chemical weapons could not function alongside their new operational doctrine of mobile, combined arms warfare.

The cooperative Soviet-German facilities would operate until 1933, when Hitler, motivated in part by his antipathy for the Soviet Union, no longer felt it necessary to hide German rearmament activities. Even though direct Soviet-German military cooperation had lasted less than a decade, its impact would prove immense. The covert German rearmament program initiated by Seeckt had laid the groundwork for a massive expansion of the German military. German corporations were prepared to begin mass production of new lines of aircraft, tanks and submarines developed from prototypes secretly tested from 1926 to 1933. For their part, the Soviets had received extensive German assistance in the crash-course industrialization that would render the Red Army the world’s largest and most mechanized military force by 1939.

The Molotov-Ribbentrop Pact, formalized on August 23, 1939, was the final culmination of a two-decade crusade by both sides to arm themselves, eliminate the postwar order established at Versailles and destroy their mutual enemy, Poland. The resumption of military cooperation played a vital role in reforming the interwar alliance. Stalin, who had begun personally directing Soviet naval construction in 1936, made sure that the Soviet military received vast quantities of German military technology in the Molotov-Ribbentrop Pact in exchange for Soviet raw materials. Germany again began to send its officers to the Soviet Union to advise and assist the Soviets in training and technical development. Further, in the fall of 1939, the Germans agreed to supply Soviet submarines fighting against Finland, while the Soviets did the same for German commerce raiders. At the height of cooperation, Stalin even granted the German Navy permission to open a secret naval base near Murmansk to interdict British shipping and assist in the invasion of Norway. Only with the German invasion of the Soviet Union would the last of the joint ventures be terminated.

Though largely forgotten today, interwar Soviet-German military cooperation reshaped the European balance of power. By the end of September 1939, Germany and the Soviet Union shared a border, a capacity for making war, and an ideological framework of annihilation. Through their alliance, Germany gained the space to rebuild its army and develop new technologies of war. In return, the Soviet Union received vital military, technological, and economic assistance. The stage was set for World War II.

The Soviet-German Pact illustrates why the post-World War I order failed. It also offers some potent lessons for the present. The Inter-Allied Commissions of Control, the watchdog established to supervise German disarmament, delivered its final ominous report in January 1927:

Germany has never disarmed, has never had the intention of disarming, and for seven years had done everything in her power to deceive and ‘counter-control’ the Commission appointed to control her disarmament.

Yet the Allies lacked the political willpower to effectively end Germany’s secret rearmament programs. American policymakers were indifferent. British leaders tended to be sympathetic to Germany in the 1920s. Further, both British and American businesses were eager to exploit economic opportunities in Germany and the Soviet Union. France showed some inclination to halt German military resurgence, but lacked the power to act alone. This lack of strategic harmony among the victors hamstrung any efforts to preserve the status quo.

The postwar state of affairs was particularly damaged by the technological successes of Soviet-German cooperation. The limitations of the Treaty of Versailles failed to block the advance of German military technology primarily because of the Reichswehr’s work in Russia. In fact, the Reichswehr actually saved money on the research and development process through its secret, small-scale prototype production and testing program. A combination of industrial espionage, willing business partners outside of Germany, and cooperation with the Soviet Union enabled Germany to keep pace with military developments elsewhere at a fraction the cost of other military establishments. The failure of Western leaders to recognize this fact meant that they vastly underestimated the technical abilities of the German military during the crises of the late 1930s. The Soviet-German partnership makes clear the immense difficulty in halting the military-technological development of pariah states. In a world where the United States seeks to enforce nuclear non-proliferation and slow the military-technological advance of its geostrategic foes, the lessons of the interwar Soviet-German partnership remain valuable.

Ian Johnson received his Ph.D. from the Ohio State University in 2016. His dissertation was entitled “The Faustian Pact: Secret Soviet-German Military Cooperation in the Interwar Period.” He is currently a doctoral fellow with International Security Studies at Yale University.

Image: Hans Still, WarRelics.eu