By 13 February, 3rd Belorussian Front had pushed 4th Army out of the Heilsberg triangle. After 13 March 3rd Belorussian Front had pushed 4th Army into a ten by two mile beachhead west of Heiligenbeil before Hitler finally allowed the army to retreat across the Frisches Haff to the Frische Nehrung on 29 March. After Königsberg fell, Hitler sent Headquarters, 4th Army, out of East Prussia and merged its units with 2nd Army to form the East Prussian Army Group, commanded by Dietrich von Saucken, which surrendered to the Red Army at the end of the war in May. Meanwhile, the Headquarters, 4th Army became Headquarters, 21st Army.