Nevertheless, development continued in order for the nascent German military to gain experience with multi-turreted tanks. In 1934 Rheinmetall built two mild steel prototypes, both with their own turret design. Three more prototypes were built with proper armor and the Krupp turret in 1935 and 1936. The "Großtraktor" was later put into service for a brief period with the 1 Panzer Division; the "Leichttraktor" remained in testing until 1935. In the late 1920s and early 1930s German tank theory was pioneered by two figures: General Oswald Lutz and his chief of staff, Lieutenant Colonel Heinz Guderian. Guderian became the more influential of the two and his ideas were widely publicized. Like his contemporary Sir Percy Hobart, Guderian initially envisioned an armored corps ("panzerkorps") composed of several types of tanks. This included a slow infantry tank, armed with a small-caliber cannon and several machine guns. The infantry tank, according to Guderian, was to be heavily armored to defend against enemy anti-tank guns and artillery. He also envisioned a fast breakthrough tank, similar to the British cruiser tank, which was to be armored against enemy anti-tank weapons and have a large 75-millimeter (2.95 in) main gun. Lastly, Germany would need a heavy tank, armed with a massive 150-millimeter (5.9 in) cannon to defeat enemy fortifications, and even stronger armor. Such a tank would require a weight of 70 to 100 tonnes and was completely impractical given the manufacturing capabilities of the day. In the early 1930s, the German Army called upon a few German firms to put together some funded prototype light and medium tanks. At this time, the Army did not have a formal plan of action in terms of what it realistically needed. Light tanks could be made available in large quantities for a relatively low price while medium tanks afforded firepower but came at a price. At any rate, the German industrial infrastructure - both the post-war limitations and the economical hit caused by the crash of 1929 - made the call easy for the Germany Army - the pursuit would be for the development of light tanks to start with. In 1931, Major-General Oswald Lutz was appointed the "Inspector of Motor Transport" in the German Army (Reichswehr) with Heinz Guderian as his Chief of Staff and they began building the German Armored Forces and a program of light training tank to train future personnel of Panzer Divisions.