This fourth documentary in the "Why We Fight" propaganda series, shown in theaters across America during World War II to inform the public and rally support for the Allied troops, focuses on the harrowing bombardment of England by the Nazis in 1940. Using a combination of staged and real footage, director Frank Capra details the exploits of the heroic RAF pilots who fought the German Luftwaffe over the skies of London, and celebrates the courage of the British during their "darkest hour."