On Dec. 29, 1941, almost three weeks after the Japanese attack on Pearl Harbor that plunged the United States into World War II, President Franklin D. Roosevelt, in one of his famous "fireside chats," told Americans: "We must become the Arsenal of Democracy."

With that directive, he marshaled the economic might of the nation to an epic display of mass production the world had never known. By the time the war -- the greatest in the history of human conflict -- was over, American engineers and assembly-line workers had built 124,000 ships, 300,000 war planes, 41 billion rounds of ammunition, 100,000 tanks and armored cars, 2.4 million military trucks, 434 millions tons of steel and 36 billion yards of cotton textiles.

In tackling this prodigious task Michigan, then with only 4% of the nation's population, obtained more than 10% of nearly $200 billion in major contracts by the U.S. and foreign governments from June 1940 to September 1945.

Wayne, Washtenaw, Oakland and Macomb counties accounted for more than 70% of the state's production. And of Detroit, historian Alan Clive wrote: "No American city . . . carried out more war work." Engineers in the metropolitan Detroit area made a monumental contribution to Allied victory, more than vindicating FDR's historic exhortation.

Their success traces back to World War I when, even without Mr. Roosevelt's ringing exhortation to inspire them, they made their first contributions to an Allied victory in history's first global conflict.

After the war erupted in 1914, Detroit factories took munitions orders from England, France and other European governments. Consequently, the entry of the United States into the conflict in 1917 found several factories ready to step up to a wartime footing. "Practically every plant of any size was swung over to this business," records a City of Detroit historical account. "And in spite of the fact that approximately 60,000 skilled workmen left for the fighting front, the industrial army at home was near 275,000."

Nuts & bolts of power

America's entry into the first World War sent into battle Detroit's highly developed system of standardization, high tolerances and interchangeability -- the nuts and bolts of mass production. The automobile industry, lacking any experience in military manufacturing, unleashed a flood of trucks, ambulances, field-kitchen trailers, artillery subassemblies, tanks, airplanes airplane engines and submarine chasers. This material tipped the war decisively in favor of America's exhausted allies and established the United States as a world power.

Railroad-equipment-builder American Car & Foundry Co. was one of the first Detroit factories to get into defense work. In 1915 it began filling orders for artillery shells from Britain. France had a contract with the Dodge Brothers to build recoil mechanisms for howitzers. Buick was building subassemblies for tanks and tractors for Britain. And Packard was developing the Liberty aircraft engine.

In 1917, when the U.S. became a co-belligerent, American Car went on three shifts a day to make shells. The Ford, Lincoln, Dodge and General Motors plants joined with Packard to mass-produce 8- and 12-cyl. Liberty aircraft engines. Fisher Body built airplane fuselages, and the Ford plant at River Rouge constructed Eagle subchasers for the Navy. GM also turned out 20,000 trench-mortar shells a month while 90% of its truck production went off to war. The army adopted the Cadillac V-8 as its standard staff car. And the Buick Model 16AA ambulance became as familiar on European battlefields as the "Jeep" would become two decades later.

Auto companies were the first to become involved in making products for what would become World War II. They supplied Britain and France with war material during the 1930s without interrupting the production of cars and trucks for the domestic market. But following Pearl Harbor, they confronted the daunting task of totally reconverting all their facilities to war work.

Within days of the Dec. 7 attack, the government charged the auto companies with building 75% of all aircraft engines, more than one-third of all machine guns, nearly 80% of the tanks and tank parts, half of the diesel engines and all of the motorized units for the army.

The reconversion of the auto industry was mastermined by William S. Knudsen, a former GM president.

Most auto builders date their transformation to a memorable meeting in Detroit on Oct. 25, 1940. Everyone who had anything to do with the manufacture of automobiles attended -- from primary producers, parts and appliance fabricators to tool and die makers.

Mr. Knudsen outlined principles and practices for farming out subcontracts. And when America entered the war, these principles enormously streamlined the participation of thousands of small industries in the national defense program.

Mr. Knudsen announced that he intended to use the auto industry to back up the airplane industry. As a result, DeSoto, Chrysler, Hudson and Goodyear Rubber Co. were soon building a long line of parts for Glenn L. Martin Co. of Baltimore. Murray Corp. did the same for Boeing's B-17 Flying Fortress. and Fisher Body Div. of GM backstopped partsmaking for North America.

Within months, engineers and designers from GM, Ford and Chrysler and from hundreds of parts and subcontracting firms swarmed through the plants of the aircraft industry. They made rough sketches, took notes and soaked up airplane expertise and know-how.

Consequently, two years after the Pearl Harbor attack the auto industry was turning out:

* Complete B-24, Grumman TBF Average and F4F Wildcat aircraft and Waco CG4 gliders;

* Parts for the B-17, Martin B-26, North American Mitchell B-25, Curtiss SB2C Hell Diver, Douglas A-20 Boston, Curtiss C-46 Commando, Consolidated C-87 Express, Douglas C-64 Skymaster and Vought OS2U Kingfisher;

* Engines for the North American P-51 Mustang, Curtiss BT-14 Valiant, and for Britain's Avro Lancaster, DeHavilland Mosquito and Vickers-Supermarine Spitfire.

On Jan. 20, 1942, the newly created War Production Board halted production of passenger cars and light trucks. Thereafter, auto engineers spent the war mass-producing products to vanquish the Axis powers.

They turned their brains and hands to making arms and ammunition, military vehicles, artillery and airplanes and equipment ranging from the gyro-compasses and rangefinders to top-secret devices for atomic bombs.

The honor roll in this colossal undertaking is extensive. A few citations must stand proxy for the many.

Ford fabricated the biggest airplane plant in the world -- Willow Run, MI, which built four-engined B-24 Liberator bombers. A mile long, quarter-mile wide and costing $100 million, the plant was larger than the combined prewar plants of the major airplane manufacturers of the day -- Boeing, Douglas and Consolidated. The facility built in excess of 8,500 Liberators -- more than one every hour.

Chrysler constructed its tank arsenal in Warren, MI, in 10 months and began shipping units by September 1941. The arsenal built more than 25,000 tanks.

Mass production of the Browning .30-caliber machine gun went to GM's Brown-Lipe-Chapin, AC Spark Plug, Frigidaire and Saginaw Steering divisions. In mid-November 1940, Saginaw produced its first model -- seven months ahead of schedule. In March 1942, when the contract called for delivering 280 weapons, Saginaw shipped 28,728 -- and dropped the price per copy from $667 to $141.44.

In tackling production of the famous Swedish-designed Oerlikon cannon, Pontiac Div. engineers virtually redesigned the entire piece. Their simplified breech casing cut machine time from 240 hours to 90. The new design reduced total production time by 35 hours and trimmed $166 from the unit cost.

Packard engineers completely redrafted the blueprint for Britain's Rolls-Royce Merlin aircraft engine. They did so in order to achieve the one-tenthousandths-of-an-inch tolerances demanded by Detroit's mass producers. Packard delivered the first nine Merlins at a cost of $6.25 million, with the company "reaping" a profit of $6,206 on the deal.

From Sept. 1, 1939, when the war erupted in Europe, until August 1945, when Japan surrendered, the auto industry delivered almost $50 billion worth of war material. Nearly 40% of it consisted of aircraft and aircraft parts, about 30% was military vehicles and parts, and 13% went into tank production. Marine equipment, guns, artillery and ammunition were among the other major items.

Among the unsung heroes of the home front were the Detroit area's many small war plants -- those with less than 500 employees. "Without these plants, it would have been impossible for the plane factories, tank arsenals, truckmakers and shipyards to achieve their production goals," said M.A. Holmes, regional director of the Smaller War Plants Corp.

"The average American thinks of war production in terms of finished bombers, tanks, guns and ships. He forgets that each of these major items contains perhaps hundreds of parts and subassemblies produced by concerns whose names wouldn't even be recognized."

Brains & brawn

Detroit brains and production expertise stepped into the breech during lesser wars in Korea (1950-'53) and Vietnam (1964-'75).

Within weeks of the invasion of South Korea by its northern neighbor, Ford, Buick and Nash were negotiating with the Department of Defense for the production of Pratt & Whitney engines for B-36 Convair bombers, Boeing B-50 medium bombers, and Fairchild C-119 and Douglas C-124 transport aircraft.

In the first year of the war, Detroit received the bulk of $7.6-billion worth of contracts awarded to Michigan. Ford built a plant in Livonia, MI, to produce M-48 tanks. Packard constructed a facility in Utica, MI, to manufacture jet engines. Among the principal holders of contracts for tactical vehicles were GM (2 1/2-ton trucks), Dodge (ambulances) and Fruehauf (light and heavy trailers).

The $7.6-billion figure represented the peak of military expenditures in Michigan during the Korean war. And it is well worth noting that in this conflict, the government spent 9.5% of all its military procurement funds in Michigan -- primarily in the metropolitan Detroit area. (The comparable fraction for World War II was 10.5%.)

Three years later, when the armistice agreement was concluded, the state's defense spending -- the bulk of which continued to be concentrated in metropolitan Detroit -- fell to approximately $650 million annually.

In mid-1966, when America escalated its military involvement in Vietnam, millions of added dollars were pumped into the Detroit metropolitan area for the purchase of trucks, "jeeps," engines and M-60 tanks. That year, the state's defense contracts hit $1 billion, a peak not recorded since the Korean conflict, with Detroit once again getting the bulk of the work.

In 1971, as U.S. participation in the Vietnam war was in its decline, Chrysler was working on a $52 million order for M-60 tanks, and GM had a $34 million contract for automobile engines, spare parts, armored personnel carriers, trucks and M-16 rifles.

And in 1991, the unique human and industrial resources of the Detroit metropolitan area went into action once again on the side of the U.S. and its allies. M1A1 Abrams battle tanks built by General Dynamics in the Sterling Heights arsenal outfitted U.S. Army armored spearheads executing Gen. Norman Schwarzkopf's epic left hook around the opposing forces, ending the Gulf War after 100 hours of ground-based hostilities.

As demanding as the production feats recorded during the Korean and Vietnam wars were, the auto industry once again demonstrated its amazing flexibility by delivering the goods without interrupting the flow of vehicles for the nation's civilian market.

Experts say that modern technology has profoundly altered military strategies and doctrine as they would apply to world wars of the future. So it seems unlikely that the auto industry will ever again face a production demand as prodigious as that of World War II. Be that as it may, many recall those momentous years as Detroit's finest hour.

For Michigan and the United States, it was "probably the greatest collective achievement of all time," wrote Donald F. Nelson, chairman of the War Production Board. "No other such ... effort was ever attempted by the human race."