In December 1941, the United States entered World War II, and the U.S. government soon after launched the "Rosie the Riveter" propaganda campaign encouraging women to pitch in with the war effort. Before the war began, women already comprised a quarter of the American workforce and eventually overtook a third of U.S. jobs by 1945. During that period 3 million women worked at war plants as the real-life Rosie the Riveters, building aircraft bombers, tanks, guns and even American flags for military activities. The Library of Congress has preserved photographs of these power-tool-wielding, manual-laboring ladies of World War II in its archives. This gallery of women workers showcases the diversity of jobs they fulfilled, as well as some of the finer details of female life in massive midcentury factories.