Ross Gunn (May 12, 1897 – October 15, 1966) was an American physicist who worked on the Manhattan Project during World War II.

During World War II he was involved in the development of thermal diffusion technology for isotope separation.

After the war Gunn became director of the Weather Bureau's Physical Research Division, where he carried out a series of studies into atmospheric phenomena.

During summer vacations he worked as a radio operator on the SS Seeandbee, a passenger ship on the Great Lakes, and for the Glenn L. Martin Company.

He returned to his studies when the war ended, his income supplemented by work as an instructor, and received his Bachelor of Science in Electrical Engineering (BSEE) degree from the University of Michigan in 1920.

The experience at McCook convinced him that he had been too hasty in abandoning his studies, so that year he quit to take a job as an instructor at Yale University, where he was placed in charge of the High Frequency laboratory at the physics department.

[2] In August 1927, Gunn accepted a position with the Naval Research Laboratory (NRL), becoming assistant superintendent of the Heat and Light Division in 1928.

He could choose his own topics of research, and chose to study natural phenomena such as cosmic rays and terrestrial and solar magnetism.

[4] Niels Bohr had theorized that only the uranium-235 isotope was fissile, so the first step was to determine a means of separating it from the more abundant uranium-238.

In June 1944, the Manhattan Project decided to take it up, and constructed the S-50 thermal diffusion plant at the Clinton Engineer Works in Oak Ridge, Tennessee.

His citation read:For exceptionally distinguished service to the United States Navy in the field of scientific research and in particular by reason of his outstanding contribution to the development of the atomic bomb ... For his untiring devotion to this most urgent project, Dr. Gunn has distinguished himself in a manner richly deserving of the Navy’s highest civilian award.

Bowen and Commodore Deak Parsons arranged for naval personnel, including Hyman Rickover, to be assigned to the Manhattan Project to learn about the new technology.