Warren developed the technique of producing stereoscopic images of the breast with X-rays while working in the Department of Radiology at the University of Rochester School of Medicine.

He led a survey team from the Manhattan Project to assess the effects of the atomic bombings of Hiroshima and Nagasaki.

In 1946 he was Chief of the Radiological Safety Section of the Joint Task Force for Operation Crossroads, the nuclear test at Bikini Atoll.

[4] Warren was one of the original group that Dean George Whipple assembled to staff the new medical school.

[13] In February 1943, Warren met with Dr Albert K. Chapman, the vice president and general manager of Eastman Kodak, Brigadier General Leslie R. Groves, the director of the Manhattan Project and Colonel James C. Marshall, the commander of the Manhattan Engineer District (MED).

Friedell had joined the Metallurgical Laboratory in August 1942 from the University of California, Berkeley, where he had been involved in radiology research under Dr Robert S. Stone.

In October, Groves penned a letter to the Surgeon General of the United States Army, Major General Norman T. Kirk, requesting that he cooperate with the Manhattan Project in furnishing medical supplies, providing funds for medical care of military personnel, and directly commissioning Warren and other doctors at specified ranks.

This letter was signed by Lieutenant General Brehon B. Somervell and delivered in person by Colonel Kenneth D. Nichols, who had replaced Marshall as the district engineer.

Warren's initial task was to staff hospitals at Oak Ridge, Richland, Washington, and Los Alamos, New Mexico.

This presented an enormous challenge, because workers were handling a variety of toxic chemicals, using hazardous liquids and gases under high pressures, working with high voltages used in novel ways, and performing experiments involving explosives, not to mention the largely unknown dangers presented by radioactivity and handling fissile materials.

[18] Warren was personally responsible for the safety aspects of the Trinity nuclear test on 16 July 1945 at Alamogordo, New Mexico.

On 11 August, Groves phoned Warren and ordered him to organize a survey team and proceed to Guam, and thence to Japan to evaluate the effect of the atomic bombs and take measures to insure the safety of Allied troops occupying the cities.

Initially the survey team was to accompany the assault troops of the III Amphibious Corps and the V Amphibious Corps in the invasion of Japan, but Japan surrendered on 14 August, the day the survey team departed San Francisco by air.

Warren's party, equipped with portable geiger counters, arrived in Hiroshima by air on 8 September as part of a group headed by Brigadier General Thomas F. Farrell that also included Brigadier General James B. Newman Jr and Japanese Rear Admiral Masao Tsuzuki, who acted as a translator.

Some 42,000 personnel were deployed to Bikini Atoll as part of Admiral William H. P. Blandy's Joint Task Force 1 to conduct the test.

Warren, as Chief of the Radiological Safety Section (RADSAFE), planned and implemented measures to assess, limit and control the impact of radiation.

Teams were given special training at Oak Ridge in the operation of instrumentation to measure radioactivity, and the interpretation of their readings.

[22] Training was also conducted aboard USS Haven en route to Bikini Atoll, where it arrived on 12 June 1946.

He temporarily became the Chief of the Medical Section of the Atomic Energy Commission, the civilian agency which succeeded the Manhattan Project.

In 1946 the California State Legislature unanimously voted $7 million to establish the new school, and Earl Warren signed it into law.

[26][27] With Dr William P. Longmire Jr, a 34-year-old plastic surgeon from Johns Hopkins University recruited by Lawrence as professor of surgery,[28] they became the "Founding Five" of the new school.

His citation read: For the imaginative, prescient, and vigorous efforts which made possible the early development of atomic energy so as to assure the protection of man and the environment, and for the establishment of a biomedical research program which has resulted in many substantial applications of ionizing radiation to diagnosis and treatment of disease and to the general welfare.

[3] The Stafford L. Warren Medal is named in his honor and is awarded to the top graduating medical student from the David Geffen School of Medicine at UCLA each year.