In summer 1940, President Franklin D. Roosevelt appointed Patterson assistant secretary of war under Henry L. Stimson, a prominent but elderly Republican and former secretary of state and secretary of war. Patterson's mandate was to facilitate industrial procurement, manpower, and training as the U.S. military, much neglected during the 1930s, readied itself for a potential major war. Patterson worked indefatigably, showing a mastery of logistics, and in December 1940 earned promotion to undersecretary. Throughout the conflict, he made winning the war as swiftly and expeditiously as possible his overriding goal, demanding that American industrialists and workers alike devote all their energies to this end. He made a particularly effective team with his Navy Department counterpart, Undersecretary James V. Forrestal. Both men thought it essential that the United States should remain militarily strong and well-prepared after the war.
When the war ended, President Harry S Truman appointed Patterson secretary of war to replace Stimson. Patterson, convinced that the developing Cold War demanded substantial increases in American military commitments and budgets, strongly supported aid to Greece, Turkey, and other countries facing a communist threat. In the interests of efficiency, he forcefully advocated unification of the three armed services under a single secretary of defense, returning to private life when this was implemented in late 1947. Patterson died in an air crash in Elizabeth, New Jersey, on 22 January 1952.
Eiler, Keith E. Mobilizing America: Robert P. Patterson and the War Effort, 1940–1945. Ithaca, NC: Cornell University Press, 1997.; Hooks, Gregory. Forging the Military-Industrial Complex: World War II's Battle of the Potomac. Urbana: University of Illinois Press, 1991.