TB-3. The great artillery manufacturer Krupp was soon active in the south of the USSR, near Rostov-on-Don. In 1925, a flying school was established near Lipetsk (Lipetsk fighter-pilot school) to train the first pilots for the future Luftwaffe. Since 1926, the Reichswehr had been able to use a tank school at Kazan (Kama tank school) and a chemical weapons facility in Saratov Oblast (Tomka gas test site). In turn, the Red Army gained access to these training facilities, as well as military technology and theory from Weimar Germany. The Soviets offered submarine-building facilities at a port on the Black Sea, but this was not taken up. The Kriegsmarine did take up a later offer of a base near Murmansk, where German vessels could hide from the British. During the Cold War, this base at Polyarnyy (which had been built especially for the Germans) became the largest weapons store in the world. Documentation Most of the documents pertaining to secret German-Soviet military cooperation were systematically destroyed in Germany. The Polish and French intelligence communities of the 1920s were remarkably well-informed regarding the cooperation. This did not, however, have any immediate effect upon German relations with other European powers. After World War II, the papers of General Hans von Seeckt and memoirs of other German officers became available, and after the dissolution of the Soviet Union, a handful of Soviet documents regarding this were published. Relations in the 1920s Trade Since the late nineteenth century, Germany, which has few natural resources, had relied heavily upon Russian imports of raw materials. Before World War I, Germany imported of raw materials and other goods per year from Russia. This fell after World War I, but after trade agreements signed between the two countries in the mid-1920s, trade had increased to per year by 1927. In the late 1920s, Germany helped Soviet industry begin to modernize, and to assist in the establishment of tank production facilities at the Leningrad Bolshevik Factory and the Kharkov Locomotive Factory. Germany's fear of international isolation due to a possible Soviet rapprochement with France, the main German adversary, was a key factor in the acceleration of economic negotiations. On October 12, 1925, a commercial agreement between the two nations was concluded. Plans for Poland Alongside the Soviet Union's military and economic assistance, there was also political backing for Germany's aspirations. On July 19, 1920, Victor Kopp told the German Foreign