John Manley was an American physicist and a member of the Calculations Group (group T-5) at Los Alamos during the Manhattan Project.
Manley was a research associate in the Metallurgical Laboratory at the University of Chicago in 1942 when he was recruited for the Project. He was among the first group of scientists that arrived on the Hill in April 1943 and helped with construction of laboratory buildings and the installation of a Cockcroft-Walton Generator, which he brought with him from the University of Illinois.
During the Project, Manley served as one of Oppenheimer's principal aides, with particular responsibility for laboratory management. Manley worked alongside a number of well-known scientists, including I.I. Rabi, Robert Serber, and Edward Teller. He helped survey the landscape around the Trinity site before the test and witnessed the explosion from inside a wooden bunker.
After the war, he served as associate director of the Los Alamos National Laboratory. He was chairman of physics at the University of Washington in Seattle for six years, and he returned to Los Alamos as research adviser from 1957 until his retirement in 1972.