Dwight Eisenhower, the Supreme Commander of the Allied Expeditionary Force, would never forget the moment his boots hit the sand during Operation Overlord—the D-Day invasion of Normandy in 1944. Shortly after the landings, Ike toured the beaches, which were littered with broken, bullet-pierced vehicles. It looked like a junk yard of dead machinery—yet also, proof that the war was being won by the soldiers of the American workforce, on assembly lines thousands of miles away.

“There was no sight in the war that so impressed me with the industrial might of America as the wreckage on the landing beaches,” he recalled in his memoirs.

War is about valor, heroism and sacrifice. But the story of victory during Operation Overlord, and the broader war, is also one of industrialism. World War II was, in large part, a contest between the Allies and Axis powers to dream up ingenious war machines and mass produce them with unparalleled speed.

The D-Day invasion, for example, utilized some 50,000 vehicles of all types, well over 5,000 ships and more than twice that number of airplanes. There were amphibious trucks, tanks, four-wheel-drive troop transporters, flame-throwing armored cars, jeeps, fighter planes, bombers… No entity did more to produce that machinery than the American automobile industry, which at the time of World War II, had a larger economy than almost every foreign nation on earth.

Here’s a look back at how Detroit became the biggest war boomtown of them all.

William Knudsen was president of General Motors—the largest corporation in history—in 1940 when President Franklin Roosevelt charged him with heading up all military production in the U.S. So Knudsen gave up one of the most well compensated jobs in the nation to take on a government position at a salary of $1. Soon after, at the New York Auto Show, Knudsen gave a keynote speech that lit the flame of industrial Detroit. “The first half of 1941 is crucial,” Knudsen told a gathering of the most powerful Motor City executives. “Gentlemen, we must out-build Hitler.”

Knudsen went on to become a lieutenant general in the Army, the first and only civilian American to receive this honor, and those Detroit auto men became heroes in the battle of the assembly lines. As Arthur Herman wrote in his book Freedom’s Forge: How American Business Produced Victory in World War II, by the war’s end, Knudsen had gone from the president of GM to “the man who had built the U.S. armed services into the greatest military machine in history.”

In the spring of 1941, months before Pearl Harbor but well after the war had begun in Europe, Edsel Ford (Henry Ford’s only son) and Charlie Sorensen, the company’s foremost production guru, began mobilizing the most ambitious industrial project in history up to that time: a factory that could turn out the biggest, most destructive bomber in the American arsenal, the B-24 Liberator, at a rate of one per hour. Ford had never built a four-engine bomber, and aviation experts insisted it could not be done.

Construction on the Willow Run Bomber Plant began that spring and it soon became the largest factory under one roof in the world. Its goal was to apply auto-making mass-production principles to 300-plus mph, 56,000-pound (when fully loaded) bombers. The Washington Post called Willow Run “the greatest single manufacturing plant the world had ever seen,” while The Wall Street Journal called it “the production miracle of the war.”

By 1945, Ford had succeeded in building Liberators at a rate of one per hour. The company turned out a total of 8,685 B-24s. Because of Ford, the B-24 is still the most mass-produced American military aircraft of all time.

In 1940, the Army asked car companies to come up with a design for a lightweight (2,175 pounds or less), four-wheel-drive vehicle that could be mass-produced and essentially take the place of what horses had been in warfare for centuries. The vehicle had to conquer all kinds of terrain, and it had to be able to carry a 625-pound load.

Three companies built prototypes: Willys-Overland, Ford and Bantam. The first two went on to make some 660,000 “blitz buggies”—Willys built 376,397 and Ford, 282,352. Because the vehicles by both had to use interchangeable parts, they were very similar. Miraculously, the first jeep that Ford constructed—GP No.1 Pygmy—still exists; it’s on display at the U.S. Veterans Memorial Museum in Huntsville, Alabama.

As this vehicle took on the name jeep (the origin of the moniker is highly debated), it also took on a life of its own, and today it has been called the grandfather of all SUVs. The famed WWII war correspondent Ernie Pyle wrote of the jeep (just before he was killed in 1945, next to the one he had been riding in), “Good Lord, I don’t think we could continue the war without the jeep. It does everything. It goes everywhere. It’s as faithful as a dog, as strong as a mule and as agile as a goat.”

In 1940, William Knudsen telephoned K.T. Keller, the chief executive of Chrysler, and asked him if Chrysler could build tanks. “I don’t know,” came the answer. “I’ve never seen one of these things.” Soon after, Chrysler broke ground on what would come to be known as the Detroit Arsenal Tank Plant, situated in what is now the suburb of Warren. Its goal: to build swarms of tanks according to auto-making mass production principles—something never accomplished before.

Even before the factory had been completed, the first Chrysler M3 tank rolled off the assembly line. The walls of the factory were not even up, so engineers brought a steam locomotive in to keep the place warm for the workers during Michigan’s bitter winter of 1940-41. As the factory swelled to 1.25 million square feet, the company switched to M4 Sherman tanks, which were powered by a Frankenstein of a motor. Engineers took five six-cylinder engines that had been used in the Chrysler Royal and Windsor cars before the war and welded them together into one 30-cylinder motor that could pump 425-horsepower to the tank treads.

In the end, the Detroit Arsenal built more tanks than all of the Third Reich during the war years, tanks that roared through enemy lines all the way to Hitler’s Berlin.

Perhaps the most extraordinary of all of Detroit’s World War II creations was a strange vehicle that could practically walk on water. The story goes back to 1942, when GM engineers got together with a marine architect and some Army officers to solve a critical problem. The army was planning massive, highly-dangerous amphibious invasions, and there would be no port facilities for the landings. Soon a sketch was on paper for a vehicle that could launch from a ship, part the waves on propeller power, then hit the ground and drive at speeds of 50 mph, with three axles and six wheels (all-wheel drive).

While the vehicle’s technical name was DUKW (in GM’s code, D signified model year 1942; U meant amphibious; K stood for front-drive; W for two-axle rear drive), the thing came to be known as the Duck. GM built over 21,000 of them, at a cost to the government of $10,800 each, according to Michael W.R. Davis’s Detroit’s Wartime Industry: Arsenal of Democracy. At 31 feet long, the Duck could carry a payload of well over 5,000 pounds. Pairs of them were strapped together to serve as landing craft for tanks. The vehicle made its most noteworthy mark during the Normandy invasion. According to the U.S. Army Transportation Museum, between D-Day on June 6, 1944 and May 8, 1945, Ducks moved 5.05 million tons of cargo onto the continent of Europe.

Pedestrians moving past 1525 Woodward Avenue in Detroit in 1943 might have noticed something odd about the place—an inordinate amount of security surrounding the first floor of an abandoned department store. In fact, something very curious was going on inside. Chrysler engineers had set up offices for something called Project X-100, and FBI agents were patrolling the premises, as the work was so top secret, none of the engineers working on the project had any knowledge of what it was all about.

Only the top executives at Chrysler knew that the company was helping to build the atomic bomb.

“To laymen, the thing [the Manhattan Project] sounded almost incredibly fantastic,” according to Chrysler’s 1947 official history of its bomb work, entitled Secret. “But if the United States Government thought it practicable, this, [Chrysler CEO] Mr. Keller said, was all that the Corporation needed to know.”

At this laboratory on Woodward Avenue, Chrysler engineers designed diffusers—cylindrical metal containers—that would not corrode during the process of separating fissile uranium-235 from uranium-238, at the Army’s secret Oak Ridge atomic plant in Tennessee. By 1944, thousands of workers at Chrysler’s Lynch Road factory were at work building 3,500 of these diffusers. According to the Atomic Heritage Foundation, these diffusers were so well-designed, they were not only instrumental in building the Little Boy bomb used on Hiroshima, they remained in use until the 1980s.

At the time of Pearl Harbor, General Motors had dwarfed every other corporation in the world—by far. And by the end of the war, GM had become the largest military contractor in the world, responsible for more than $12 billion in war production. Tanks were rolling out of GM’s Cadillac factory, where some of the nation’s most luxurious cars were being built just a few years earlier. Oldsmobile had delivered roughly 40 million artillery rounds. Pontiac was building highly complicated Oerlikon anti-aircraft guns.

GM’s WWII production numbers (courtesy of the GM Heritage Center) tell the story: 119,562,000 artillery shells; 39,181,000 cartridge cases; 206,000 aircraft engines; 13,000 Navy fighter planes and torpedo bombers; 97,000 aircraft propellers; 301,000 aircraft gyrocompasses; 38,000 tanks and tank destroyers; 854,000 trucks; 190,000 canons; 1.9 million machine guns and submachine guns; 3.1 million carbines; 3.8 million electric motors; 11 million fuses; 360 million ball and roller bearings; 198,000 diesel engines; and more.

With the fate of the world at stake, GM played the starring role in the effort to outbuild Hitler and Hirohito. No other corporation, anywhere on earth, at any time in history, ever did more to win a war.