By late 1943 the Luftwaffe was facing multiple problems in navigation and control of its assets in the European airspace.
Allied jamming of existing VHF voice radio links and MF navigation beacons was becoming extremely effective, At the same time training of pilots was being curtailed by the lack of fuel.
This resulted in fighter formations being unable to find the allied bombers and frequently getting lost.
However a simpler system that could be rolled out faster and was usable by minimum hour pilots in single seat fighters was also developed.
Controlling a single fighter was of not much use in practice so the Luftwaffe developed group control, where a Y-Fighter was part of a group of fighters intercepting an allied bomber stream, The Y-Fighter was painted a distinctive colour and the rest of the flight simple followed him.
the system was susceptible to jamming on the FuG16ZY wavelength but was at least partially usable for the rest of the war.