Free Command and Control by Eric Schlosser

hexagons. It looked like a gigantic soccer ball and weighed about five thousand pounds.
    The shape and composition of the explosive lenses were irrelevant, however, if the lenses failed to detonate at exactly the same time. The shock wave would travel through the device at a speed of one millimeter per millionth of a second. If a single lens detonated a few ten millionths of a second before the others, it could shatter the plutonium without starting a chain reaction. Blasting caps and Primacord were the detonators usually employed with conventional explosives. But both proved incapable of setting off thirty-two charges simultaneously. The physicist Luis Alvarez and his assistant, Lawrence Johnston, invented a new type of detonator for the job—the exploding-bridgewire detonator. It sent a high-voltage current through a thin silver wire inserted into an explosive. The current vaporized the wire, created a small shock wave, and detonated the explosive. Donald F. Hornig, who was one of the youngest scientists at Los Alamos, devised a contraption, the X-unit, that could store 5,600 volts in a bank of capacitors and then send that electricity instantaneously to all the detonators.
    In theory, the X-unit and the exploding bridgewires would set off thirty-two explosive lenses at once, creating the perfect shock wave and imploding the plutonium core. In reality, these new inventions were unpredictable. Cracked insulation frequently caused the detonators to short-circuit. When that happened, they didn’t work. And a week before the Trinity test, an X-unit fired prematurely during a lightning storm. It had been triggered by static electricity in the air. The misfire suggested that a nuclear weapon could be set off by a lightning bolt.
    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, thecore 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