into the war in late 1941, with autoplants converted to military-only production of arms, munitions, trucks, tanks and planes. In the run up to the outbreak of war, the large companies engaged in tank production did not have space set aside for expanding their production lines. In consequence, unlike allied manufacturers, German tank manufacturers never came to a point where they were stockpiling and storing excess finished products. Though these companies did expand with the increased demand of the ongoing war, it was not until the assignment of Albert Speer as Minister of Armaments that true efforts were made to bring mass production techniques to the German tank production industry. During the period before the war, all companies with the exception of Alkett (which was under the control of Rhine-Metal Borsig, a subsidiary of the government-controlled Hermann Göring Works) were privately owned stock companies with the stock available for purchase by the public. All these companies, with the exception again of Alkett, produced tanks in addition to their normal peacetime manufacture of trucks, locomotives, and other heavy equipment. From 1935 onward, the government progressively increased its control over industries engaged in rearmament. The Nazi Party's Four Year Plan introduced in 1936 placed Hermann Göring in leadership of the state's efforts to bring industry into state control. Through threat and coercion Göring was able to expand the Nazi Party's control of private industry involved in steel and armament production. By 1938, this control included the rationing of essential raw materials, factory inventories, labor hours, rates of pay, working conditions, building and machine tool expansion, plant locations and stock dividends. All companies were forced to join the Economic Board of the tank industry which handled all questions affecting the industry. Location of German tank manufacturing industry The tank manufacturing industry in Germany was not concentrated in any one geographic location. Major plants were located in Nurnberg, Kassel, Brunswick, Magdeburg, and Berlin. There was, however, some geographical concentration of tank component manufacturers, such as engines and gears in Friedrichshafen, hulls, turrets, and guns in the Ruhr, rubber treads in Hanover, and instruments in Berlin. These locations, if interdicted, represented a potential choke point to German tank manufacturing. German tank problem During the course of the war the Allies made sustained efforts to determine the extent of German productivity, and approached this in two major ways: conventional intelligence gathering and statistical estimation. In many