Prior to World War II, the operational groups were recreated. Initially, in March of 1939, they consisted only of staffs formed around existing corps commands. According to the Polish mobilization scheme, they were to become mobile reserves of the Polish armies and other major strategic-scale units.
Some groups were formed during the final mobilization of late August 1939, others were formed during the war as strategic considerations necessitated. Most were attached to armies, several however were independent.