to verify Albert Einstein's mass–energy equivalence, E = mc2. Francis William Aston wrote that: In 1933, Bainbridge was awarded a prestigious Guggenheim Fellowship, which he used to travel to England and work at Ernest Rutherford's Cavendish Laboratory at Cambridge University. While there he continued his work developing the mass spectrograph, and became friends with the British physicist John Cockcroft. When his Guggenheim fellowship expired in September 1934, he returned to the United States, where he accepted an associate professorship at Harvard University. He started by building a new mass spectrograph that he had designed with at the Cavendish Laboratory. Working with J. Curry Street, he commenced work on a cyclotron. They had a design for a cyclotron provided by Ernest Lawrence, but decided to build a cyclotron instead. Bainbridge was elected a Fellow of the American Academy of Arts and Sciences in 1937. His interest in mass spectroscopy led naturally to an interest in the relative abundance of isotopes. The discovery of nuclear fission in uranium-235 led to an interest in separating this isotope. He proposed using a Holweck pump to produce the vacuum necessary for this work, and enlisted George B. Kistiakowsky and E. Bright Wilson to help. There was little interest in their work because research was being carried out elsewhere. In 1943, their cyclotron was requisitioned by Edwin McMillan for use by the U. S. Army. It was packed up and carted off to Los Alamos, New Mexico. World War II In September 1940, with World War II raging in Europe, the British Tizard Mission brought a number of new technologies to the United States, including a cavity magnetron, a high-powered device that generates microwaves using the interaction of a stream of electrons with a magnetic field. This device, which promised to revolutionize radar, demolished any thoughts the Americans had entertained about their technological leadership. Alfred Lee Loomis of the National Defense Research Committee established the Radiation Laboratory at the Massachusetts Institute of Technology to develop this radar technology. In October, Bainbridge became one of the first scientists to be recruited for the Radiation Laboratory by Ernest Lawrence. The scientists divided up the work between them; Bainbridge drew pulse modulators. Working with the Navy, he helped develop high-powered radars for warships. In May 1943, Bainbridge joined Robert Oppenheimer's Project Y at Los Alamos. He initially led E-2, the instrumentation group, which developed X-ray instrumentation for examining explosions.