This paper will describe the upgrade of the 350 kV NEMP HPD pulse generator of the WIS in Munster, Germany to an output voltage of 1.2 MV by using a commercially available 1.2 MV Marx generator. The results of a PSpice investigation of the influence of the peaker capacitance and the line inductance on the pulse rise time, amplitude and width will be presented. The design, production and testing of the HV elements as feed through, pulse line and peaking capacitor under the restrictions of a short isolation distance and a high voltage will be discussed. The paper will conclude with a presentation of the measured electrical field parameters such as rise time, field strength, reproducibility etc. reached after the integration of the modified pulse generator into the existing dipole hybrid antenna construction in Munster