Foreign Office whether "there was any possibility of combining the German and the Red Army for a joint war on Poland". This was yet another event at the start of military cooperation between the two countries, which ended before the German invasion of the Soviet Union on June 22, 1941. By early 1921, a special group in the Reichswehr Ministry devoted to Soviet affairs, Sondergruppe R, had been created. Weimar Germany's army had been limited to 100,000 men by the Treaty of Versailles, which also forbade the Germans to have aircraft, tanks, submarines, heavy artillery, poison gas, anti-tank weapons or many anti-aircraft guns. A team of inspectors from the League of Nations patrolled many German factories and workshops to ensure that these weapons were not being manufactured. Treaty of Rapallo 1922 and secret military cooperation The Treaty of Rapallo between Weimar Germany and Soviet Russia was signed by German Foreign Minister Walther Rathenau and his Soviet colleague Georgy Chicherin on April 16, 1922, during the Genoa Economic Conference, annulling all mutual claims, restoring full diplomatic relations, and establishing the beginnings of close trade relationships, which made Weimar Germany the main trading and diplomatic partner of Soviet Russia. Rumors of a secret military supplement to the treaty soon spread. However, for a long time the consensus was that those rumors were wrong, and that Soviet-German military negotiations were independent of Rapallo and kept secret from the German Foreign Ministry for some time. This point of view was later challenged. On November 5, 1922, six other Soviet republics, which would soon become part of the Soviet Union, agreed to adhere to the Treaty of Rapallo as well. The Soviets offered Weimar Germany facilities deep inside the USSR for building and testing arms and for military training, well away from Treaty inspectors' eyes. In return, the Soviets asked for access to German technical developments, and for assistance in creating a Red Army General Staff. The first German officers went to Soviet Russia for these purposes in March 1922. One month later, Junkers began building aircraft at Fili, outside Moscow, in violation of Versailles. The joint factory built Junkers' most recent all-metal designs. Russian aircraft designer learned new techniques at the factory, such as Andrei Tupolev or Pavel Sukhoi. After the factory was turned over to the Russians, Russian adaptations of the Junker bombers were manufactured there, such as the Tupolev TB-1 and Tupolev