After Japan attacked Pearl Harbor, the United States mobilized for war on an unprecedented scale. Millions of Americans enlisted to fight, and war production expanded dramatically. Scientists worked on developing new technologies like radar and the atomic bomb through secret projects like the Manhattan Project. By 1944, the Allies had begun to gain victories over German forces in Europe and North Africa, culminating in the D-Day invasion of Normandy and the liberation of Western Europe the following year. However, the war against Japan in the Pacific continued.