View images taken of pilots and crewmen during World War II. World War II (1939-1945) was the most destructive, costliest war in human history. It involved dozens of countries, spanned continents, and resulted in the death of 50 million lives. Air warfare was a key component to the battle strategies waged throughout the war. The United States Army Air Forces (USAAF or AAF) was the predecessor of today's United States Air Force, and fought in campaigns throughout the European, North African and Mediterranean, and Pacific Theaters of war.