US physicist who was director of the first atomic-bomb test at Alamogordo, New Mexico, 1945.

He also made important innovations in the mass spectrometer.

Bainbridge was born in Cooperstown, New York, and educated at the Massachusetts Institute of Technology (MIT) and Princeton University.

He worked at the Cavendish Laboratory, Cambridge, England, in the early 1930s, and held academic posts at Harvard from 1934; he also worked in the radiation laboratory at MIT 1940-43 and then in the Los Alamos laboratory on the atomic bomb until 1945.

He also carried out research in radar.

The mass spectrometer invented by English physicist Francis Aston focused ion beams of varying velocity but not varying direction.

In 1936 Bainbridge developed a machine in which ion beams that are nonuniform in both direction and velocity can be brought to a focus.