The United Kingdom, the US, the Soviet Union, and France produced significant numbers of tanks before and during World War II. The early tanks of Germany were inferior to many of their opponents' tanks in the areas of armor and firepower. However, in their tactical employment the German tanks dominated all rivals early in the war. German doctrine stressed the use of rapid movement, mission-type tactics and combined-arms where tanks operated with mobile infantry and air support; this doctrine was popularly called "Blitzkrieg". This doctrine required the Germans to equip their tanks with radios, which provided unmatched command and control for flexible employment.