The German Panzerkampfwagen Neubaufahrzeug ("new construction vehicle"—a cover name), abbreviated as PzKpfw Nb.Fz, series of tank prototypes were a first attempt to create a medium tank for the Wehrmacht after Adolf Hitler had come to power. Multi-turreted, heavy and slow, they were not considered successful, which led to only five being produced. These were primarily used for propaganda purposes and training, though three took part in the Battle of Norway in 1940. Pictures of the Neubaufahrzeuge were displayed with different turret models and orientations to fool allied spies; American and Soviet agents independently reported that the Germans had two new heavy tanks, the Panzer V and VI. In reality, these tanks were far from the Panzer V Panther and the Panzer VI Tiger. Development 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, while Krupp's turret was more rectangular and had the 3.7 cm gun mounted beside the 7.5 cm gun. Both turrets were also armed with a co-axial MG-34 machine gun, along with the two sub-turrets at the front and rear of the tank. The Neubaufahrzeug went through a series of name changes, including "Groß Traktor Nachbau", "Mittlerer Traktor Neubau", and "Neubau Fahrzeug" in 1933, and "Neubau-Panzerkampfwagen IV" in April 1940. The Neubaufahrzeug was never officially named Panzerkampfwagen V or VI. Two mild steel trial tanks were built by Rheinmetall in 1934. The first prototype used Rheinmetall's own turret design, while the second prototype used Krupp's turret design, which was mounted in 1935. Three more tanks were built in 1936 with proper armor, all mounting Krupp's turret design. The sub-turrets were also redesigned by a third contractor. The Neubaufahrzeug was intended to fulfill the role of a medium tank in Germany's developing armored force, but it proved to have too many problems with