During the 1930s, in addition to his classes at HBS, Doriot taught at the US Army Industrial College where he trained officers in the preparation of adequate military supplies and equipment. At the onset of World War II, Colonel Edmund B. Gregory (HBS MBA '29), one of Doriot's former students, chose Doriot to serve as lieutenant colonel in the Quartermaster Corps. The Corps was responsible for research and development of new materials and products for combat troops. Doriot became a naturalized US citizen in 1940 and began active duty on July 26, 1941.

Doriot held seven positions in four divisions of the Quartermaster Corps and eventually rose to the rank of brigadier general. Thereafter referred to as "the General," even in civilian life, Doriot proved tremendously adept in bringing together science and industry to create improved supplies and equipment for US soldiers. He argued, "[T]here is a complete lack of understanding of the problems of human beings and the problem of making a human being a good fighting person."²⁶

"Doriot undertook to bring together many of the country's best academic researchers, scientists, and industrial planners to support the war effort.... [T]he Military Planning Division was a key component, benefiting from what proved to be a novel cooperation among science, industry, and the military."

Christopher G. Hartman, Advance Man: The Life and Times of Harry Hoagland, 2005²⁵

While Doriot did not teach at Harvard Business School during the war, HBS instituted a number of programs with the military. From 1941 to 1943, for example, the Quartermaster Corps set up a Reserve Officers Training Corps at HBS to train officers in the preparation of military supplies, the first such program in a graduate school. In 1943, HBS completely suspended the MBA program in order to devote itself to the training of Army and Navy personnel. The same year, the US War Department established the Army Supply Officers Training School (ASOTS) at HBS, where quartermaster officers learned higher levels of responsibility for military supplies by understanding the perspectives of business and industrial organizations.²⁷

A steady stream of individuals who trained at HBS entered the Quartermaster Corps, and Doriot also reached out to HBS graduates to assist him in the war effort. William H. McLean (HBS MBA '34), Doriot's former teaching assistant, served as Doriot's chief assistant throughout the war. Henry W. Hoagland (HBS MBA '39), another student of Doriot's, also worked as an aide to Doriot in the Military Planning Division.

In an early assignment for the Motor Transportation Division, Doriot ensured the ample production of Army trucks from major car companies including Ford and General Motors. He also boosted rubber supply through a program of higher production and greater citizen conservation. In 1942, Doriot became chief of the Research and Development Branch of the Military Planning Division, where he oversaw the combined departments of production, materials conservation, and design specification of new products and equipment. The Military Planning Division's contributions to wartime products included water-repellent fabrics, cold weather shoes, uniforms, backpacks, sunscreen, insecticides, and K-rations. "[I]n wartime, [Doriot] went through a unique, intense immersion in high-stakes product development, where human lives hung in the balance," author Jeffrey Cruikshank notes. "He experienced first-hand the astonishing innovative capacities of American engineers, inventors, and tinkerers, and he also learned how difficult it was to get even great ideas off the laboratory bench and into the military 'marketplace.'"²⁸

Doriot sought out research taking place in universities such as the Harvard Fatigue Lab (housed on the HBS campus in Morgan Hall), which focused on the effects of heat, cold, and altitude in a laboratory that included a climatic room, altitude chamber, and treadmills. The Lab made over 150 recommendations concerning clothing, nutrition, and survival gear to the War Department. One recommendation included the shoepac, a boot with a rubber sole and sides, loose enough to accommodate three pairs of socks, and durable enough to withstand cold weather. Doriot relied on his vast network of contacts in diverse industries as well. He recruited Monsanto and Dow Chemical Company to help create a lightweight, fiberglass-based plastic armor, named Doron, after him. The armor consisted of plastic plates inserted into a nylon vest that covered the front and back torso and shoulders. Dow Chemical also developed Saran (used after the war as Saran Wrap) to insulate combat boots.

In recognition of his innovative work, Doriot received the Distinguished Service Medal (the highest US military medal given to non-combatants). In addition, he was decorated a Commander of the British Empire and awarded the French Legion of Honor.²⁹ "Doriot learned how to become a venture capitalist during the war," Doriot's biographer Spencer E. Ante notes, "for it was through World War II that he underwent the most significant metamorphosis of his life, transforming himself from a professor of business into a world-class builder of innovative new enterprises."³⁰ Doriot's understanding of the risks and rewards of investing in new technologies stemmed in part from his wartime experiences and would serve him well in the decades to come.