On December 2nd, 1942, scientists at the University of Chicago produced the first controlled nuclear chain reaction in human history. The experimental reactor was initially located under the university's Stagg football field. Soon after, the it was relocated to 'Sita A' in the Palos Park Forest Preserve where scientists performed further experiments and built an additional reactor as part of the Manhattan Project, the U.S. nuclear development program during World War II.
The relocation of the first reactor on Site A was the result of the search for a remote area. Today, Red Gate Woods is part of the expanded suburbs of Chicago and is not remote at all anymore. All traces of the site have disappeared after having been dismantled. The initial site built by the U.S. Army Corps of Engineers included a guard house, a dog shelter, a library, a cafeteria, a dormitory and recreational spaces in addition to the research labs and reactor control rooms on 19 acres of restricted and guarded land. The scientists who lived and worked there throughout World War II were forced to maintained a strict code of silence as the discoveries being made were critical for the success of the U.S. military atomic program.
Called 'Chicago Pile-1' (CP-1), the world's first nuclear reactor was moved from the University of Chicago to 'Site A' in the Red Gates Woods in 1943 and was renamed CP-2. The pile boasted 10 tons of uranium metal, 42 tons of uranium oxide and 472 tons of graphite. Shielding the reactor core were six inches of lead and four feet of wood.
Under the leadership of physicist Walter Zinn, the group of scientists operating on Site A performed experiments in the small laboratory on top of CP-2 in addition to constructing CP-3, the first water-cooled nuclear reactor. When the Atomic energy Commission closed Site A in 1954, the two reactors were dismantled ans buried in a forty foot deep trench on the site. Beginning in the 1980s, the Commission and the Department of Energy responded to public concern by monitoring the area and wiring to neutralise toxic radioactive materials before the reopening of the site for the public in 1991.