This is needed so that the magnetic ignition mechanism of naval mines or torpedoes are not triggered.
During the Second World War these methods of mine protection were standard for all large battle ships.
Modern MSP systems consist of a plurality of electromagnetic coils which suppress the magnetic signature in several directions.
For the majority of the vessels of the German Navy, this is done in the two magnetic measurement and treatment centers in Wilhelmshaven and Kiel.
The German Navy maintains an Earth's magnetic field simulator for this purpose in the Borgsted narrows at Schirnau-Lehmbek, in which the MSP system is adjusted accordingly for the entire vessel in various operating states and for different measured latitudes.