[1][2][3][4][5] During World War II, Johnston worked at the MIT Radiation Laboratory where he invented ground-controlled approach radar.

He later worked at the Stanford Linear Accelerator Center as head of the electronics department, and was a professor at the University of Idaho in Moscow,[6][7] where he taught until his retirement.

[8] After graduation from Hollywood High School in 1936, Johnston earned an associate degree at Los Angeles City College.

This allowed aircraft to be guided to a safe landing in adverse weather conditions, based on radar images,[8] and would later prove crucial during the Berlin Airlift.

[9] While a graduate student at Berkeley, Johnston met Mildred (Millie) Hillis, a girl who shared his strong Christian faith.

[12] At age 26 in 1944, Johnston followed Alvarez to the Manhattan Project's Los Alamos Laboratory, where Robert Oppenheimer, who was also from the University of California, was the director.

Because of the high level of spontaneous fission in reactor plutonium, it was decided to use a nearly critical sphere of the metal and compress it quickly into a much smaller and denser core using explosives, a technical challenge at the time.

Using conventional explosive techniques with blasting caps, progress towards achieving simultaneity to within a small fraction of a microsecond was discouraging.

[9] Johnston and Alvarez's next task for the Manhattan Project was to develop a set of calibrated microphone/transmitters to be parachuted from an aircraft to measure the strength of the blast wave from the atomic explosion, so as to allow the scientists to calculate the bomb's energy.

He observed the Trinity nuclear test from a B-29 Superfortress that also carried fellow Project Alberta members Harold Agnew and Deak Parsons.

[15] Flying in the B-29 Superfortress The Great Artiste in formation with the Enola Gay, Alvarez and Johnston measured the blast effect of the Little Boy bomb which was dropped on Hiroshima.

Under Alvarez's supervision, he wrote his PhD thesis at the Lawrence Berkeley Laboratory on the "Development of the Alvarez-type proton linear accelerator".