He was recalled to military service as the commander of Army Group A on 10 September 1939 but retired again on 21 September 1939. During World War II, Hammerstein-Equord was involved in several plots to overthrow Hitler, including in the run up of the failed plot of 20 July 1944. He tried repeatedly to lure Hitler into visiting a fortified base under his command along the Siegfried Line of the Western Front. He confided to retired former army chief of staff and leading conspirator Colonel-General Ludwig Beck that "a fatal accident will occur" when the Führer visited his base. Hitler never accepted Hammerstein-Equord's invitation. Instead, he was transferred to command in Wehrkreis (Defense District) VIII in Silesia, then relieved of his command on personal orders by Hitler for his "negative attitude towards National Socialism". He became active in the German Resistance.