Explore a Hidden History

Albert Einstein meets with Leo Szilard to compose a cautionary letter to President Franklin D. Roosevelt. Photo courtesy of the U.S. Department of Energy
In nuclear fission, uranium-235 is bombarded with neutrons, causing its nucleus to split into krypton, barium, several neutrons, and a large amount of energy.
The “Fat Man” plutonium bomb exploding over Nagasaki, Japan on August 9, 1945. Photo courtesy of the National Archives and Records Administration
The Manhattan Engineer District’s insignia, adopted in 1945, symbolizes a lightning bolt splitting an atom.

The building of an atomic bomb during World War II, code-named the Manhattan Project, was one of the most significant and secretive undertakings of the 20^th century. Notably, the Project has just marked its 70^th anniversary. A little-known fact is that hidden operations were scattered across the country. Explore New York City’s sites with our interactive map, timeline, brief project history, and resources from A Guide to the Manhattan Project in Manhattan by the Atomic Heritage Foundation.

In a world where threats to international stability affect not only relationships among nations but conditions impacting global civilian populations, Carnegie Corporation’s International Peace and Security program presents this website as a historical lens on nuclear security and weapons issues.