 In 1941, he was sent to the Soviet Union to instruct Russian pilots in flying lend-lease P-40 Tomahawks.In February 1942, after the United States' entry into World War II, Zemke desired to join a USAAF unit and made his way back to the United States through Iran and Egypt.After several temporary assignments, including tests of the new P-47 Thunderbolt, Zemke, by then a major, became group commander of the 56th Fighter Group—the first fighter group to fly the P-47—on September 16, 1942, preparing it for movement to England.