vehicles, tanks or similar machines, which may be turned to military use". Despite the manpower and technical limitations imposed upon the German Army by the Treaty of Versailles, several Reichswehr officers established a clandestine General Staff to study World War I and develop future strategies and tactics. One such Reichswehr officer, Hans von Seeckt, became Commander-in-Chief. Seeckt took to heart the lessons learned in the Great War and set about in rewriting the foundation of the German Army. Infantry still remained the heart and soul of any planned offensive, but the tank would become the spearhead of actions that could shatter enemy defenses through speed, force and firepower. Tactics involved the splitting up of enemy formations and counteractions involving pincer movements to surround and ultimately decimate the enemy in whole. By 1926, German Army doctrine was all rewritten to fulfill this vision. Although at first the concept of the tank as a mobile weapon of war met with apathy, German industry was silently encouraged to look into tank design, while quiet cooperation was undertaken with the Soviet Union. In the late 1920s and early 1930s, Germans closely co-operated with Russians in the development of armored vehicles, which were tested at Kama tank school, near Kazan in the USSR. There was also minor military cooperation with Sweden, including the extraction of technical data that proved invaluable to early German tank design. As early as 1926 various German companies, including Rheinmetall and Daimler-Benz, produced a single prototype armed with a large 75-mm gun (codenamed Großtraktor, "large tractor", to veil the true purpose of the vehicle). Only two years later prototypes of the new Leichttraktor ("light tractor") were produced by German companies, armed with 37-millimeter KwK L/45 guns. Development of the Neubaufahrzeug started in 1932 when Wa Prüf 6 established design specifications for a new 15 tonne tank to be known as the "mittlere Traktor". It had many connections to the previous Großtraktor, utilizing many of the same components including the engine and transmission. Initially both Krupp and Rheinmetall were asked to submit proposals, but after the end of trials of the Großtraktor prototypes, during which Rheinmetall's vehicle proved superior to others, Krupp would only be awarded a contract for a turret design while Rheinmetall was to design both a chassis and turret. Rheinmetall's turret design had a rounded shape and was armed with a 3.7 cm gun above the 7.5 cm gun,