Defeated and occupied in 1939, Poland had suffered under the Nazi heel for nearly five years. Undaunted, however, the Poles formed an underground army, the Armia Krajowa (Home Army), and waited for a moment of German weakness. That moment seemed to have arrived in July 1944 as the Soviet armies began to advance into eastern Poland. The AK launched its revolt in Warsaw on 1 August 1944. Though its 5,000 fighters achieved some initial successes, the Germans were able to retain control over both the Vistula River bridges and the airbase, dooming the revolt to isolation and defeat. The SS was put in charge of suppressing the rebellion, beginning a wave of atrocities shocking even by Eastern Front standards.