Dr. Freeman K. Hill, 71, a retired physicist with the Johns Hopkins University Applied Physics Laboratory in Laurel and an expert in supersonic aerodynamics, died of cancer March 6 at his home in Fulton, Md.

Dr. Hill joined the APL in 1942 and supervised tests of the proximity fuses that were developed for artillery shells in World War II. In 1947, he began using hypersonic wind tunnels to simulate the flights of guided missiles.

He served in APL's research center from 1954 to 1963, then joined its aeronautics division. From 1978 until he retired in 1981, he worked on a project designed to convert ocean thermal energy into electricity.

Dr. Hill was born in Portland, Ore. He graduated from Reed College and earned a doctorate in physics at the University of Washington.

He received the Navy Department's Ordnance Development Award and a Certificate of Merit from the Office of Scientific Research and Development for his work on the proximity fuse.

Dr. Hill was a member of the American Physical Society, the American Institute of Aeronautics and Astronautics, the Washington Academy of Science, and the Washington Philosophical Society.

Survivors include his wife, Swananoa, of Fulton; a son, Freeman, of Virginia Beach, and three grandsons.