Development of the Neubaufahrzeug (German
for "new construction vehicle") started in 1933 when the then
Reichswehr gave a contract for the development of a Grobtraktor (heavy tractor)
to both Rheinmetall and Krupp. Grosstractor was a codename for the development
of a heavy tank, Germany being still forbidden to develop tanks under the terms
of the Treaty of Versailles.
The two designs resembled each other to a
great extent, the main difference being the weapons placement. Each had a main
turret armed with a 75 mm KwK L/24 main gun and secondary 37 mm KwK L/45.
Rheinmetall's design mounted the second gun above the 75 mm KwK L/24, while the
Krupp design had it mounted next to the 75 mm KwK L/24. Both designs had a
secondary turret mounted to the front and the rear of the main turret. These
turrets were slightly adapted Panzer I turrets, with the standard machinegun armament.
Rheinmetall's design was designated the PzKpfw
NbFz V ('PanzerKampfwagen NeubauFahrzeug V'), and the Krupp design the PzKpfw
NbFz VI. It was intended that these designs would fulfill the role of heavy
tank in the armored forces, but the design proved to be too complex and
unreliable for this role. Development nevertheless continued in order for the
nascent German military to gain experience with multi-turreted tanks.