Jagdschloss, officially the FuG 404, was the designation of a German early warning and battle control radar developed just prior to the start of World War II.

Although it was built in limited numbers, Jagdschloss is historically important as the first radar system to feature a plan position indicator display, or "PPI".

The PPI effort started fairly early in the history of radar; Hans Hollmann of Telefunken filed a patent for the multi-phase electrostatic deflection in a cathode-ray tube "along a conical surface of revolution" "such as required in practice for instance for the feeding of certain directional antenna systems, or the like" in 1936.

It mounted a large antenna consisting of two rows of four half-wave dipoles aligned horizontally, rotating on a shaft located at the top of the tower.

Although the system demonstrated its utility, further units were not ordered until the fall of 1942, likely due to the increasing tempo of RAF Bomber Command's night offensives at that time.

Range was also increased from the original 150–300 km (93–186 mi; 81–162 nmi), which required an improvement in the angular resolution in order to maintain the ability to resolve aircraft.

The return signal was slightly delayed, appearing as a second "blip" on the radar screen, allowing the operator to visually identify friendly aircraft.