World War I brought mechanized warfare to the battlefield, and with it carnage on a scale never seen before. To deal with the mass casualties in the trenches of Europe, a Yale professor turned to those keystones of American industrial might, the assembly line and mobility, to deliver lifesaving medical care to American troops at the front lines in a new way.

The mobile medical units born during the Great War were the innovation of Joseph Marshall Flint, M.D., Yale’s first full-time professor of surgery. Flint volunteered as a surgeon on the Western Front in France in 1915, two years before the United States joined the war, both to provide care and to learn. Based on what he witnessed there, Flint proposed a unit unlike any on U.S. military organizational charts: a compact organization that would move with battles and treat the most serious casualties.

Flint came to Yale in 1907 and supported “whole-time” clinical training that combined research, teaching and clinical care. As a professor of anatomy, the 1900 graduate of Johns Hopkins was an unconventional choice to head the surgery program. Perhaps to prove his surgical skills to his colleagues, Flint signed on as surgeon for an Athens hospital during the Greco-Bulgarian War in 1913, then served as a wartime surgical chief in Passy, France. There, he observed mobile war units originated by the French.

With the United States contemplating war, Flint proposed a new kind of unit: it would be “a surgical machine on the Ford Factory principle which has a sufficient operating capacity to care for all of the cases at one time,” he wrote in a report to the government from the front. The report, along with other papers pertaining to Flint’s work, are in the Manuscripts and Archives collection of the Yale University Library.

At its 1917 Commencement, in an era when universities sponsored military units, Yale announced a $250,000 grant to fund the Yale Mobile Operating Unit No. 39—the first such unit for the American Expeditionary Forces and a prototype for other mobile units. Yale doctors, nurses and would-be ambulance drivers bombarded Flint with applications. He warned his 15 officers, 19 nurses and 80 enlisted men that the new unit faced unknown dangers. Indeed, the ship carrying the Yale unit zigzagged through wreckage in the Irish Sea before being attacked by submarine on September 14, 1917. Flint, then 45, wrote with uncharacteristic emotion: “No amount of training or propaganda could have equaled this experience in developing detestation of inhuman methods employed by the enemy.”

Flint prepared meticulous plans for the unit: patients arrived by truck or train, moving through wards—shock, X-ray and operating tents—in one direction only. The one-way system minimized not only confusion, but infection. “The organization of the wards was such that no patient could be neglected,” Flint explained.

Heading to the front in April 1918, the unit worked in trenches within sight of the Germans. It witnessed its most intense activity with the St. Mihiel offensive in autumn 1918. “Patients began to arrive by truckloads,” wrote orderly Stanley Daggett, a 1917 alumnus of Yale College. During the first 24 hours of one battle, the unit admitted 170 cases requiring surgery.

Flint received the Distinguished Service Medal for his research and service. Returning from Europe with a chronic infection, he resigned from Yale in 1920. He died in 1944, as Yale’s 39th General Hospital Unit regrouped in the Pacific, caring for the wounded of World War II.