The United States of America entered World War II on December 7, 1941, following the Japanese attack on Pearl Harbor. Initially, the active combat zone of the US Air Force was the Pacific Ocean, the North Atlantic and the Mediterranean, but soon they began hostilities in continental Europe. In addition to supporting and providing cover for ground forces and ships of the navy, the aircraft carried out bombardments of strategic targets in the depths of the Axis countries. Over time, these bombings became permanent. During the war years, American industry was able to organize the mass production of combat aircraft with high tactical and technical characteristics. By the end of the war, the USAAF had grown into a high-profile military force with 2,400,000 strong.