The United States Antarctic Service Expedition (1939–1941), often referred to as Byrd’s Third Antarctic Expedition, was an expedition jointly sponsored by the United States Navy, State Department, Department of the Interior and The Treasury. Although a U.S.-government sponsored expedition, additional support came from donations and gifts by private citizens, corporations and institutions.

Richard Evelyn Byrd Jr., an American naval officer, was a pioneering American aviator, polar explorer, and organizer of polar logistics. Aircraft flights in which he served as a navigator and expedition leader crossed the Atlantic Ocean, a segment of the Arctic Ocean, and a segment of the Antarctic Plateau. He is also known for discovering Mount Sidley, the largest dormant volcano in Antarctica.