There was a desire to have heavy tanks with the reforming German Army and development of the Neubaufahrzeuge (NbFz) (new construction vehicle) was done by Krupp and Rheinmetall. In 1934 - 1935 prototypes were ordered.
The vehicles were initially designated the PzKpfw V and PzKpfw VI. When they weren't selected for production those designations were used for the later Panther and Tiger.
Both the Neubaufahrzeuges had secondary turrets, one at the right front, and one at the left rear.