John Henry Manley (July 21, 1907 – June 11, 1990) was an American physicist who worked with J. Robert Oppenheimer at the University of California, Berkeley before becoming a group leader during the Manhattan Project.
He was born in 1907 in Harvard, Illinois. He graduated with a BS from the University of Illinois in 1929 and received his PhD in physics from the University of Michigan 1934. He was a lecturer Columbia University and later professor at the University of Illinois from 1937 to 1942. He married Kathleen, and had two daughters: Kim Manley of Los Alamos, New Mexico; and Kathleen Manley of Greeley, Colorado
By the time World War II broke out, Manley was at the University of Chicago's Metallurgical Laboratory. In 1942, his friend and colleague, J. Robert Oppenheimer, held a meeting with several leading theorists at UC Berkeley. The topic of the meeting: develop preliminary plans to design and build a nuclear weapon. Manley, one the attendees, was tasked with learning more about the properties of fast neutrons.
Less than a year later, the center of the project had shifted to the Los Alamos National Laboratory. On April 4, 1943, Manley arrived at the laboratory. Manley spent his first days in Los Alamos working with other newcomers on the construction of laboratory buildings. He also installed a Cockcroft–Walton generator, which he had brought with him from Urbana. Throughout the war Manley served as one of Oppenheimer's principal aides, with particular responsibility for laboratory management.
After the war, Manley left Los Alamos to serve as executive secretary of the general advisory committee for the Atomic Energy Commission, a federal agency charged with managing the nation's atomic assets. After leaving the AEC, he returned the Los Alamos as assistant director for research. From 1951 to 1957, Manley taught physics at the University of Washington. He retired in 1974, and died in 1990 in Los Alamos at age 82.