Harold Fidler was an Army major and a civil engineer for the Corps of Engineers. Fidler began working at the Radiation Laboratory at Berkeley with Ernest O. Lawrence in the early stages of the Manhattan Project.
Fiddler was responsible for sending weekly reports on the progress that scientists were making to Colonel James C. Marshall, who oversaw the Manhattan Project during its initial stages. Fiddler also ensured that the laboratory received the materials that it needed.
After the war, Fidler remained at the Radiation Laboratory and was appointed Associate Director in 1958.