Radar

[UKönig]

It works, just, not very well.
The electronics industry in Nazi Germany was in a deplorable state of neglect. One of the main reasons the u boats lost the war, was because the allies developed sonar and Radar detectors to such a degree that the Germans (Doenitz) didn't think possible.
German radar sets and warning receivers (while sophisticated for the time) were generally crude and unreliable instruments. Any one of a hundred reasons could interfere with the operation of the equipment, including poorly insulated or grounded wiring, waves washing over the tower causing shorts, or even strong weather could snap the delicate 'biscay cross' like a twig.
The first models were big bulky units bolted to the conning tower, and could only scan 15° bow left to bow right. If the target was outside that range, then it disappeared from the scope. So in order to scan a full circle, it would be necessary to turn the sub 360°, a time consuming process under normal conditions, impossible to perform during battle.
A lot of skill and finesse is required for success of the endeavor.
So you, Herr Kaleun, aren't always doing it wrong, you just have dodgy gear.