Command and Control

At eighteen past three in the afternoon on July 13, 1945, the plutonium core was delivered to a steel tower a couple of miles from the McDonald Ranch House. The tower rose about a hundred feet above the desert and resembled an oil rig with a small shed on top. The rest of the nuclear device sat inside a tent at the base of the tower, awaiting completion. At first, the core wouldn’t fit inside it. For a few minutes, nobody could understand why, and then the reason became clear. The plutonium was warm, but the housing that it was supposed to enter had been cooled by the shade of the tent. Once the housing warmed, the core easily slid in. At about four o’clock, a thunderstorm threatened, and the tent started to flap violently in the wind. The small group of scientists left the base of the tower and waited for half an hour at the ranch house until the storm passed. When they returned, Kistiakowsky supervised the placement of the last explosive lenses, and at dusk the device was bolted shut. The next morning, as it was slowly hoisted to the top of the tower, surplus Army mattresses were stacked to a height of fifteen feet directly beneath it, in case the cable broke.

The nuclear device was an assortment of spheres within spheres: first, an outer aluminum casing, then two layers of explosives, then a thin layer of boron and plastic to capture neutrons that might enter from outside the core, then more aluminum, then a tamper of uranium-238 to reflect neutrons that might escape from inside the core, then the ball of plutonium, and finally, at the very center, the golf ball — size neutron initiator — a mixture of beryllium and polonium that would flood the device with neutrons, like a nuclear fuse, when the shock wave from the lenses struck. Inside the metal shed atop the tower, the detonators were installed by hand, two for every explosive lens, linked to a pair of X-units. The device now looked like something concocted in a mad scientist’s laboratory — a six-foot-tall aluminum globe with a pair of large boxes, the X-units, attached to it and thirty-two thick electrical cables leaving each box, winding around the sphere, and entering evenly spaced holes on its surface.

The Trinity test was scheduled for four in the morning on July 16, but forecasters predicted bad weather. Going ahead with the test could prove disastrous. In addition to the threat of lightning, high winds and rain could carry radioactive fallout as far as Amarillo, Texas, three hundred miles away. Postponing the test had other drawbacks: the device could be damaged by the rain, and President Harry S. Truman was in Potsdam, Germany, preparing to meet with Winston Churchill, the British prime minister, and Joseph Stalin, the general secretary of the Soviet Union’s Communist Party. Nazi Germany had recently been defeated, and Truman was about to demand an unconditional surrender from the Japanese. Having an atomic bomb would make it easier to issue that demand. General Groves argued that the test should go forward, as planned, and Oppenheimer agreed. Both men became increasingly nervous, on the evening of the fifteenth, not only about the weather but also about the risk of sabotage. And so Donald Hornig was instructed to “babysit the bomb.”

At 9:00 P.M., Hornig climbed to the top of the hundred-foot tower as rain began to fall. He brought a collection of humorous essays, Desert Island Decameron. His reading was interrupted by the arrival of a violent electrical storm. Atop the tower in a flimsy metal shed, Hornig sat alone with the book, the fully armed device, a telephone, and a single lightbulb dangling from a wire. He was twenty-five years old and had recently earned a Ph.D. in chemistry at Harvard. Having designed the X-unit, he knew better than anyone how easily it could be triggered by static electricity. Whenever he saw a lightning bolt, he’d count the seconds — one — one thousand, two — one thousand, three — one thousand — until he heard the thunder. Some of the lightning felt awfully close. At midnight, the phone rang, and Hornig was told to come down. Hornig did so, gladly, in the pouring rain. He was the last person to see the device.