'Fuchs' was a German uncompleted undertaking to provide for the disengagement of General Friedrich Hossbach’s 4^th Army of Generaloberst Georg-Hans Reinhardt’s Heeresgruppe 'Mitte' in East Prussia, where it was hard pressed by General Ivan D. Chernyakhovsky’s 3^rd Belorussian Front and Marshal Sovetskogo Soyuza Konstantin K. Rokossovsky’s 2^nd Belorussian Front, for movement to the west to become part of Reichsführer-SS Heinrich Himmler’s Heeresgruppe 'Weichsel' (21/22 January 1945).

The first stage of this undertaking was the withdrawal of the 4^th Army on 21/22 January 1945 toward the 'Heilsberg-Stellung' in the south-eastern part of East Prussia. The defences of the 'Heilsberg triangle' had been built in the 1920s to allow for the defence of Königsberg by the small land forces which were all that Germany was allowed at the time.