Gerald Maurice Clemence (16 August 1908 — 22 November 1974) was an American astronomer, who spent most of his career (1930-1963) at the U.S. Naval Observatory. He was a member of the National Academy of Sciences is best known for his general theory of the motion of Mars. Subsequently, he was research associate and professor of astronomy at Yale University.
He became Director of the Nautical Almanac Office February 28, 1945 and remained in that position until Jan 31, 1958, when he became the first modern Scientific Director of the Naval Observatory, 1958-1963.
He chaired the National Academy of Science review of the U.S. Air Force Condon Report on unidentified flying objects. The other members were H.R. Crane (University of Michigan), Mark Kac (Rockefeller University), Francis Reichelderfer (former director of the U.S. Weather Service), Wallace Fenn (University of Rochester), William Rubey (University of California at Los Angeles), H. Keffer Hartline (Rockefeller University), C.D. Shane (Santa Cruz, CA), E.R. Hildgard and Oswald Villard (Stanford University) . They observed
We are unanimous in the opinion that this has been a very creditable effort to apply objectively the relevant techniques of science to the solution of the UFO problem. The Report recognizes that there remain UFO sightings that are not easily explained. The Report does not suggest, however, so many reasonable and possible directions in which an explanation may eventually be found, that there seems to be no reason to attribute them to an extraterrestrial source without evidence that is much more convincing. The Report also shows how difficult it is to apply scientific methods to the occasional transient sightings with any chance of success. While further study of particular aspects of the topic (e.g., atmospheric phenomena) may be useful, a study of UFOs in general is not a promising way to expand scientific understanding of the phenomena. On the basis of present knowledge the least likely explanation of UFOs is the hypothesis of extraterrestrial visitations by intelligent beings. 
- Review of the University of Colorado Report on Unidentified Flying Objects by a Panel of the National Academy of Sciences, National Academy of Sciences, 1969