Japan was one of the Axis powers in World War II. Its attack on Pearl Harbor, HI, on December 7, 1941 brought the US formally into the war. Japan also attacked British, Dutch, and American possessions in the Southwest Pacific around the same time.
A little-known operation of the Manhattan Engineering District took place behind enemy lines in occupied Europe. Code-named the "Alsos" Mission, these intelligence-gathering operations moved with the advancing Allies to learn firsthand how close Germany was to developing its own atomic weapon. Under the command of General Leslie Groves, these operations succeeded in capturing most of the key German scientists, stores of uranium ore and other nuclear raw materials, and thousands of research documents regarding the development of atomic energy.