Joseph Hirschfelder was an American physicist.
He held doctorates in physics and chemistry from Princeton University. He led Group E-8 (Interior Ballistics) in the Ordnance and Engineering Division at Los Alamos during the Manhattan Project. He initially worked on the design of the Thin Man plutonium bomb.
After the war, he served as chief phenomenologist at the atomic bomb tests at Bikini. Hirschfelder retired in 1981 as the Homer Adkins professor emeritus of chemistry at the University of Wisconsin at Madison. He was a member of the National Academy of Sciences and the recipient of numerous awards.