The story begins with a letter from Albert Einstein to Franklin D. Roosevelt in 1939. The celebrated physicist warned the president that Nazi Germany was developing the makings of an atomic bomb.

Roosevelt knew what would happen if Hitler got such a weapon. The president ordered a massive secret project to make sure the U.S. beat him to it. Scientists from all over the country were enlisted in the effort.

Early in 1942 Enrico Fermi and a team of physicists gathered at the University of Chicago's Metallurgical Laboratory. Their goal was to develop a self-sustaining nuclear pile. This was the first step needed to produce the bomb.

Put simply, the scientists would arrange graphite blocks and uranium pellets in a certain way. Since nobody knew what would happen when the pile was finished, control rods were inserted as a safety measure.

A new lab for the project was being built in suburban Argonne. Then the construction workers went on strike. Fermi decided to push ahead without delay, using a room under the stands of Stagg Field, the university's unused football stadium. Since the university president probably would have vetoed the location, he was not told about it.

On the afternoon of December 2, after a hearty lunch, Fermi and his team tested the pile. The control rods were slowly withdrawn. The reactions of the materials were measured. Fermi made his calculations using the most advanced equipment available--a six-inch slide rule.

The scientists were nervous. If the pile got out of control, there might be an explosion, or a radiation leak, or any number of possibilities that hadn't even been imagined. Still Fermi pressed on, adjusting the rods and trying different variables. After four-and-a-half minutes, he gave the order "Zip in!"

"There was a small cheer," one of the team recalled. "The experiment was a success."

The atomic age was launched. Later Argonne Laboratory was finished, and Fermi's team moved out of its cramped quarters under the football grandstand. Argonne is currently operated by the U.S. Department of Energy.

Back at the university, Stagg Field was eventually torn down to make way for a library. Today the site of the world's first self-sustaining nuclear reaction is marked with a sculpture--shaped like a mushroom cloud.