The Manhattan Project was a top-secret research and development undertaking during WWII that produced the first nuclear weapons. Led by the United States with support from the UK and Canada, the project was directed by General Leslie Groves and scientific director J. Robert Oppenheimer. It involved over 130,000 people and cost nearly $2 billion (about $30 billion today), with major facilities at Los Alamos, Oak Ridge, and Hanford. The project was spurred by fears that Nazi Germany was also developing atomic bombs. On July 16, 1945, the first atomic device, 'The Gadget,' was successfully detonated at the Trinity Site in New Mexico. This breakthrough changed the nature of warfare forever and provided the U.S. with the weapon that would ultimately lead to Japan's surrender.