How Detroit Went from Motor City to the Arsenal of Democracy

Detroit already had car manufacturing capability: that turned into war production capability in the early 1940s

A woman marks a bombardier enclosure for a B-24 Liberator bomber at the Ford Willow Run plant. Detroit Public Library

On this day in 1941, workers in Ypsilanti, Michigan started clearing hundreds of acres of land.

They were beginning preparations for the construction of Willow Run, a huge World War II aircraft manufacturing plant owned by the Ford Motor Company. By the end of the war, Willow Run had produced more than 8,600 B-24 bombers, writes, “and the plant’s mass-production techniques were hailed as a symbol of American ingenuity.” It was the first big factory built in a World War II push that turned Detroit and its automakers into weapons-makers. 

"Perhaps the most amazing thing was the speed in which they changed over from cars to war machines," Ford's corporate historian, Bob Kreipke, told Scott Burgess for MotorTrend. Before war broke out in Europe in 1939, Detroit was a car city, he writes, and the leaders of General Motors, Ford and Chrysler were "car men, pushing metal down assembly lines." America's military was ranked 19th in the world, behind Portugal. 

 Then, in a December 1940 fireside chat, FDR referred to America as “the great arsenal of democracy.” In the same speech, Roosevelt called for the United States to supply the Allied forces with weapons, planes, trucks and tanks. “For us this is an emergency as serious as the war itself," he said. "We must apply ourselves to our task with the same resolution, the same sense of urgency, the same spirit of patriotism and sacrifice as we would show were we at war." 

The Willow Run factory, located about 30 miles from the city, contributed to Detroit’s burgeoning reputation as a leader in the effort to support Allied troops via production. A year later, after Pearl Harbor, the United States was at war. But in the meantime, another giant, state-of-the-art factory had been built near Detroit: the Detroit Tank Arsenal.

Because Detroit already had a large automobile industry with factories ready to produce vehicles using relatively-new assembly-line techniques, it was well-suited to producing war machines. At the start of America's war, writes the Detroit Historical Society, as many as 350,000 workers moved to Detroit to work in factories producing war equipment.

"Carmakers built everything," writes Burgess: "tanks, airplanes, radar units, field kitchens, amphibious vehicles, jeeps, bombsights and bullets. Billions and billions of bullets. Detroit, with two per cent of the population, made ten per cent of the tools for war."  The area around Detroit in this period was particularly known for two innovative war machines: airplanes and tanks.

At the Willow Run plant, workers of both genders worked on airplanes, most notably the B-24 “Liberator,” which this propaganda film notes required more than production know-how than “a relatively simple automobile.”

B-24 Liberator Willow Run Assembly Plant

“Even the conception of a plant such as this was viewed with considerable skepticism,” the announcer declares. “But the people at Ford have vision as well as skill. They have always planned and worked at a broad scale.”

This is the other side of the war effort in Detroit: automakers like Ford and Chrysler, which oversaw the creation of the Detroit Tank Arsenal, made gains from the war effort. They became more visible and worked with government contracts, but the war effort also led to huge advancements in assembly-line technology, Burgess writes. For instance, "Chrysler had been tasked with building 40mm anti-aircraft guns, known as Borfors guns, which initially took 450 man-hours to build. By the end of the war, Chrysler cut that time to 10 man-hours." After the war, he writes, those skills meant that "consumers would see a large number of new car styles and frequent changes." 

Although tanks were not new inventions, World War II was the first time that entire battles had been fought with them, writes Jake Hendricks for a Michigan Technological University blog on military history. America’s first big effort at developing its own tank skills was at a giant plant in Warren, Michigan, constructed after Chrysler president K.T. Keller was asked by the War Department if his company could build a tank. "He gave a resounding 'yes,'" Burgess writes, "before asking, 'What's a tank look like?'

“By any standard," writes Kevin Thornton in his history of Detroit and tank production, the factory was "an impressive feat of construction."

Not only that: coming out of the Great Depression, giant production factories such as these demonstrated “what could happen when government and business united in a joint cause,” he writes. “On the eve of American involvement in an even more terrible war, [the Arsenal] promised strength.”

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