Even before the outbreak of war in 1939, a group of American scientists-many of them refugees from fascist regimes in Europe-became concerned with nuclear weapons research being conducted in Nazi Germany. In 1940, the U.S. government began funding its own atomic weapons development program, which came under the joint responsibility of the Office of Scientific Research and Development and the War Department after the U.S. entry into World War II. The U.S. Army Corps of Engineers was tasked with spearheading the construction of the vast facilities necessary for the top-secret program, codenamed "The Manhattan Project " (for the engineering corps' Manhattan district).