In 1940 Johnson had an operation to reset his collarbone, and began flying regularly. He took part in the offensive sweeps over German-occupied Europe from 1941 to 1944, almost without rest. Johnson was involved in heavy aerial fighting during this period. His combat tour included participation in the Dieppe Raid, Combined Bomber Offensive, Battle of Normandy, Operation Market Garden, the Battle of the Bulge and the Western Allied invasion of Germany. Johnson progressed to the rank of group captain by the end of the war.