World War II is the considered the heyday of military insignia and patches. The Army Air Forces (AAF) continued the optional wear of flight jacket patches and expanded the practice to coveralls worn by maintenance personnel.
The AAF “Hap Arnold” insignia was approved in February 1942 and authorized for wear as a SSI for all AAF members. In March 1943, the first Numbered Air Force insignia were approved and patches were made for wear by their assigned personnel.
Unofficial morale patches were also made and worn by AAF personnel. Patches were highly popular not just among service personnel but also the general public.
By the time World War II ended in 1945, millions of patches were produced for service members.