Eric Schlosser - Command and Control

The B-52 had struck the ice at a speed of almost six hundred miles per hour, about seven miles west of Thule. The high explosives of the four hydrogen bombs fully detonated upon impact, and roughly 225,000 pounds of jet fuel created a large fireball. For five or six hours, the fire burned, until being extinguished by the ice. When the first Explosive Ordnance Disposal team arrived at the site two days later, using flashlights and traveling from Thule on a dogsled, they found a patch of blackened ice about 720 yards long and 160 yards wide. Pieces of the bombs and the plane were scattered across an area of three square miles. The pieces were small — and highly radioactive. Tiny particles of plutonium had bonded with metal and plastic debris, mixed with jet fuel, water, and ice. Plutonium had risen in the smoke from the fire and traveled through the air for miles.

The one-point safety tests of the Mark 28’s core, performed secretly at Los Alamos during the Eisenhower administration, had been money well spent. If the Mark 28 hadn’t been made inherently one-point safe, the bombs that hit the ice could have produced a nuclear yield. And the partial detonation of a nuclear weapon, or two, or three — without any warning, at the air base considered essential for the defense of the United States — could have been misinterpreted at SAC headquarters. Nobody expected the Thule monitor to destroy Thule. Instead, the Air Force had to confront a less dangerous yet challenging problem: how to decontaminate about three square miles of ice, about seven hundred miles north of the Arctic Circle, during the middle of winter, in the dark.

Generators, floodlights, a helicopter pad, sleds, tracked vehicles, and half a dozen prefabricated buildings were brought to the crash site. New roads from the base were cut through the snow. A “Hot Line” was drawn around the contaminated area, with restrictions on who could enter it and decontamination control points for everyone who left it. Once again hundreds of young airmen walked shoulder to shoulder, looking for bomb parts and pieces of a B-52. Most of the debris was small, ranging from the size of a dime to that of a cigarette pack. Some of it had fallen through a gash in the ice, cut by the crash, that later refroze. The ice was about two feet thick; the water below it six hundred feet deep. Pieces of the bomb and the plane were carried away by the current or settled on the bottom of Bylot Sound.

Arctic storms with high winds complicated the recovery and cleanup efforts, spreading plutonium dust and hiding it beneath the snow. But the levels of contamination were more accurately measured at Thule than at Palomares. A new device, the Field Instrument for the Detection of Low-Energy Radiation (FIDLER), looked for the X-rays and gamma rays emitted by plutonium, instead of the alpha particles. Those rays traveled a longer distance and passed through snow. Over the next eight months, the top two inches of the blackened ice within the Hot Line were removed, trucked to the base, condensed, packed in containers, shipped to Charleston, South Carolina, and then transported by rail to the AEC facility in Aiken. The radioactive waste from Thule filled 147 freight cars.

During the summer of 1968, after Bylot Sound thawed, a Navy submersible searched for part of a Mark 28 bomb. The plutonium cores of the primaries in all four weapons had been blown to bits, and most of the uranium from their secondaries had been recovered. But a crucial piece of one bomb was still missing, most likely the enriched uranium spark plug necessary for a thermonuclear blast. It was never found — and the search later inspired erroneous claims that an entire hydrogen bomb had been lost beneath the ice.

The Air Force did a much better job of handling the press coverage at Thule than at Palomares. It helped that the B-52 had crashed near one of the most remote military installations in the world, far from any cities, towns, or tourists. An accident that contaminated three square miles of a large metropolitan area would have gained more attention. The Air Force admitted, from the outset, that nuclear weapons had been involved in the crash. Dozens of journalists were flown to Thule within days of the accident and supplied with a good deal of information. Few had the desire to remain in the Arctic for long. And a couple of other news stories — the seizure of the USS Pueblo by North Korea and the Tet offensive in Vietnam — quickly pushed Thule off the front page.

The Air Force account of the accident, however, was deliberately misleading. Denmark had imposed a strict ban on nuclear weapons, and its NATO allies were forbidden to bring them into Danish territory or airspace. For more than a decade, the Strategic Air Command had routinely violated that prohibition at Thule. The B-52 that crashed onto the ice, the Pentagon told reporters, had been on a “training flight” and had radioed that it was preparing to make an emergency landing. A handful of people within the Danish government and its military were no doubt aware that B-52s had been flying nuclear weapons over Danish territory every day for almost seven years. But they may not have known that atomic bombs were stored in secret underground bunkers at Thule as early as 1955. Hydrogen bombs were deployed there the following year. Before the introduction of SAC’s airborne alert, Thule was a convenient spot for American bombers to land, refuel, and pick up their weapons en route to the Soviet Union. The early hydrogen bombs were so heavy that prepositioning them in Greenland would allow SAC’s planes to make the long round-trip flight to Russia over the North Pole. Dozens of antiaircraft missiles with atomic warheads were later placed at Thule to defend the base from a Soviet attack. But none of these facts were shared with the Danish people.

The airborne alert program was terminated the day after the Thule accident. The risks no longer seemed justifiable, and many B-52s were now being used to bomb Vietnam. SAC’s ground alert was unaffected by the new policy. Hundreds of planes, loaded with hydrogen bombs, still sat beside runways all over the United States, ready to take off within minutes. And a B-52 secretly continued to fly back and forth above Thule, day and night, without nuclear weapons, just to make sure it was still there.

TWENTY-THREE YEARS AFTER Sandia became a separate laboratory, it created a nuclear weapon safety department. An assistant to the secretary of defense for atomic energy, Carl Walske, was concerned about the risks of nuclear accidents. He had traveled to Denmark, dealt with the aftermath of the Thule accident, and come to believe that the safety standards of the weapons labs were based on a questionable use of statistics. Before a nuclear weapon could enter the stockpile, the odds of its accidental detonation had to be specified, along with its other “military characteristics.” Those odds were usually said to be one in a million during storage, transportation, and handling. But the dimensions of that probability were rarely defined. Was the risk one in a million for a single weapon — or for an entire weapon system? Was it one in a million per year — or throughout the operational life of a weapon? How the risk was defined made a big difference, at a time when the United States had about thirty thousand nuclear weapons. The permissible risk of an American nuclear weapon detonating inadvertently could range from one in a million to one in twenty thousand, depending on when the statistical parameters were set.

Walske issued new safety standards in March 1968. They said that the “probability of a premature nuclear detonation” should be no greater than one in a billion, amid “normal storage and operational environments,” during the lifetime of a single weapon. And the probability of a detonation amid “abnormal environments” should be no greater than one in a million. An abnormal environment could be anything from the heat of a burning airplane to the water pressure inside a sinking submarine. Walske’s safety standards applied to every nuclear weapon in the American stockpile. They demanded a high level of certainty that an accidental detonation could never occur. But they offered no guidelines on how these strict criteria could be met. And in the memo announcing the new policy, Walske expressed confidence that “the adoption of the attached standards will not result in any increase in weapon development times or costs.”