 In such a weakened state, the Army Group staff planned a new position to its rear that would shorten the front lines by twenty-five percent and remove the Soviet threats posed in many salients on the current lines.The plan "Operation Blue" called for a January withdrawal of over 150 miles to the natural defensive barrier formed by the Narva and Velikaya Rivers and Lakes Peipus and Pskov.This position, the so-called "Panther Line", was buttressed by fortifications that had been constructed since September.