When built in 1941, Willow Run was the biggest factory in the world, and maybe still is: 1.25 miles long, covering some 5 million square feet. It was here that Ford built the B-24 Liberator bomber in such quantities that one every 55 minutes came off the line.
That plane was instrumental in winning World War II, as Willow Run taught the world how to mass-produce complex machines with tremendous speed and accuracy. There’s a great video here of the process and the glory days, when some 42,000 people worked there.
The development of Willow Run played several roles in the history of the automobile as well. The foundations of lean production were created there, and after the war Toyota studied American methods, including those at Willow Run, and created a system that changed automaking forever.