 Complete the following phrase:  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 