On 21 January 1968, an aircraft accident, sometimes known as the Thule affair or Thule accident (; Danish: Thuleulykken), involving a United States Air Force (USAF) B-52 bomber occurred near Thule Air Base in the Danish territory of Greenland. The aircraft was carrying four B28FI thermonuclear bombs on a Cold War "Chrome Dome" alert mission over Baffin Bay when a cabin fire forced the crew to abandon the aircraft before they could carry out an emergency landing at Thule Air Base. Six crew members ejected safely, but one who did not have an ejection seat was killed while trying to bail out. The bomber crashed onto sea ice in North Star Bay, Greenland, causing the conventional explosives aboard to detonate and the nuclear payload to rupture and disperse, resulting in radioactive contamination of the area.
The United States and Denmark launched an intensive clean-up and recovery operation, but the secondary stage of one of the nuclear weapons could not be accounted for after the operation was completed. USAF Strategic Air Command "Chrome Dome" operations were discontinued immediately after the accident, which highlighted the safety and political risks of the missions. Safety procedures were reviewed, and more stable explosives were developed for use in nuclear weapons.
In 1995, a political scandal arose in Denmark after a report revealed the government had given tacit permission for nuclear weapons to be located in Greenland, in contravention of Denmark's 1957 nuclear-free zone policy. Workers involved in the clean-up program campaigned for compensation for radiation-related illnesses they experienced in the years after the accident.
Thule Monitor Mission
In 1960, the United States Air Force (USAF) Strategic Air Command (SAC) began Operation Chrome Dome, a Cold War airborne alert program devised by General Thomas S. Power to fly nuclear-armed Boeing B-52 Stratofortress bombers to the borders of the Soviet Union. The flights were scheduled to ensure that twelve bombers were aloft at all times. These bombers gave SAC offensive capability in the event of a Soviet first strike. Beginning in 1961, B-52 bombers also secretly flew as part of the "Hard Head" mission (or "Thule Monitor Missions") over Thule Air Base. The objective of "Hard Head" was to maintain constant visual surveillance of the base's strategically important Ballistic Missile Early Warning System (BMEWS), which provided early warning of Soviet missile launches. This ensured that, if the communication link between North American Aerospace Defense Command and the base was severed, then the aircraft crew could determine if the interruption resulted from an actual attack or a mere technical failure. The monitoring mission started when the designated aircraft reached a waypoint at 75°0′N 67°30′W / 75.000°N 67.500°W in Baffin Bay and entered a figure-eight holding pattern above the air base at an altitude of 35,000 feet (11,000 m).
In 1966, United States Secretary of Defense Robert McNamara proposed cutting "Chrome Dome" flights because the BMEWS system was fully operational, the bombers had been made redundant by missiles, and $123 million ($1.22 billion as of 2025) could be saved annually. SAC and the Joint Chiefs of Staff opposed the plan, so a compromise was reached whereby a smaller force of four bombers would be on alert each day. Despite the reduced program and the risks highlighted by the 1966 Palomares B-52 crash, SAC continued to dedicate one of the aircraft to monitoring Thule Air Base. This assignment was without the knowledge of civilian authorities in the United States, who SAC determined did not have the "need to know" about specific operational points.
Broken Arrow
On 21 January 1968, a B-52G Stratofortress, serial number 58-0188, with the callsign "HOBO 28" from the 380th Strategic Aerospace Wing at Plattsburgh Air Force Base, New York was assigned the "Hard Head" mission over Thule and nearby Baffin Bay. The bomber crew consisted of five regular crew members, including Captain John Haug, the aircraft commander; Radar navigator Major Frank Hopkins; and Electronic warfare officer Captain Richard Marx. Also aboard were the co-pilot, Leonard Svitenko, a substitute navigator (Captain Curtis R. Criss) and a mandatory third pilot (Major Alfred D'Amario).
Before take-off, D'Amario placed three cloth-covered foam cushions on top of a heating vent under the instructor navigator's seat in the aft section of the lower deck. Shortly after take-off, another cushion was placed under the seat. The flight was uneventful until the scheduled mid-air refueling from a KC-135 Stratotanker, which had to be conducted manually because of an error with the B-52G's autopilot. About one hour after refueling, while the aircraft was circling above its designated area, Captain Haug directed co-pilot Leonard Svitenko to take his rest period. His seat was taken by the spare pilot, D'Amario. The crew was uncomfortable because of the cold, although the heater's rheostat was turned up, so D'Amario opened an engine bleed valve to draw additional hot air into the heater from the engine manifold. Because of a heater malfunction, the air barely cooled as it traveled from the engine manifold to the cabin's heating ducts. During the next half-hour, the cabin's temperature became uncomfortably hot, and the stowed cushions ignited. After one crew member reported smelling burning rubber, they looked for a fire. The navigator searched the lower compartment twice before discovering the fire behind a metal box. He attempted to fight it with two fire extinguishers, but could not put it out.
At 15:22 EST, about six hours into the flight and 90 miles (140 km) south of Thule Air Base, Haug declared an emergency. He told Thule air traffic control that he had a fire on board and requested permission to perform an emergency landing at the air base. Within five minutes, the aircraft's fire extinguishers were depleted, electrical power was lost and smoke filled the cockpit to the point that the pilots could not read their instruments. As the situation worsened, the captain realized he would not be able to land the aircraft and told the crew to prepare to abandon it. They awaited word from D'Amario that they were over land, and when he confirmed that the aircraft was directly over the lights of Thule Air Base, the four crewmen ejected, followed shortly thereafter by Haug and D'Amario. The co-pilot, Leonard Svitenko, who had given up his ejection seat when the spare pilot took over from him, sustained fatal head injuries when he attempted to bail out through one of the lower hatches.
The pilotless aircraft initially continued north, then turned left through 180° and crashed onto sea ice in North Star Bay at a relatively shallow angle of 20 degrees—about 7.5 miles (12.1 km) west of Thule Air Base—at 15:39 EST. The conventional high explosive (HE) components of four 1.1 megaton B28FI thermonuclear bombs detonated on impact, spreading radioactive material over a large area in a manner similar to a dirty bomb.
Haug and D'Amario parachuted onto the grounds of the air base and made contact with the base commander within ten minutes of each other. They informed him that at least six crew ejected successfully and the aircraft was carrying four nuclear weapons. Off-duty staff were mustered to conduct search and rescue operations for the remaining crew members. Owing to the extreme weather conditions, Arctic darkness, and unnavigable ice, the base relied largely on the Thule representative of the Royal Greenland Trade Department, Ministry of Greenland, Jens Zinglersen, to raise and mount the search using native dog sled teams. Three of the survivors landed within 1.5 miles (2.4 km) of the base and were rescued within two hours. For his initial actions and later services, Zinglersen received the Air Force Exceptional Civilian Service Medal on 26 February 1968 at the hands of the U.S. Ambassador, K. E. White. Gunner Staff Sergeant Calvin Snapp, who was first to eject, landed 6 miles (9.7 km) from the base—he remained lost on an ice floe for 21 hours and suffered hypothermia in the −23 °F (−31 °C) temperatures, but he survived by wrapping himself in his parachute.
An aerial survey of the crash site immediately afterwards showed only six engines, a tire and small items of debris on the blackened surface of the ice. The accident was designated a Broken Arrow, or an accident involving a nuclear weapon but which does not present a risk of war.
Project Crested Ice
The resulting explosion and fire destroyed many of the components that had scattered widely in a 1-mile (1.6 km) by 3-mile (4.8 km) area. Parts of the bomb bay were found 2 miles (3.2 km) north of the impact area, indicating the aircraft started to break-up before impact. The ice was disrupted at the point of impact, temporarily exposing an area of seawater approximately 160 feet (50 m) in diameter; ice floes in the area were scattered, upturned and displaced. South of the impact area, a 400-foot (120 m) by 2,200-foot (670 m) blackened patch was visible where fuel from the aircraft had burned—this area was highly contaminated with JP-4 aviation fuel and radioactive elements that included plutonium, uranium, americium and tritium. Plutonium levels as high as 380 mg/m2 were registered in the area.
American and Danish officials immediately launched "Project Crested Ice" (informally known as "Dr. Freezelove"), a clean-up operation to remove the debris and contain environmental damage. Despite the cold, dark Arctic winter, there was considerable pressure to complete the clean-up operation before the sea ice melted in the spring and deposited further contaminants into the sea.
Weather conditions at the site were extreme; the average temperature was −40 °F (−40 °C), at times dropping to −76 °F (−60 °C). These temperatures were accompanied by winds of up to 89 miles per hour (40 m/s). Equipment suffered high failure-rates and batteries worked for shorter periods in the cold; operators modified their scientific instruments to allow the battery packs to be carried under their coats to extend the batteries' lifespan. The operation was conducted in arctic darkness until 14 February, when sunlight gradually began appearing.
A base camp (named "Camp Hunziker" after Richard Overton Hunziker, the USAF general in charge of the operation) was created at the crash site; it included a heliport, igloos, generators and communications facilities. A "zero line" delineating the 1-mile (1.6 km) by 3-mile (4.8 km) area in which alpha particle contamination could be measured was established by 25 January, four days after the crash. The line was subsequently used to control decontamination of personnel and vehicles. An ice road was constructed to Thule from the site. This was followed by a second, more direct road so that the ice on the first road was not fatigued by overuse. The camp later included a large prefabricated building, two ski-mounted buildings, several huts, a decontamination trailer and a latrine. These facilities allowed for 24-hour operations at the crash site.
The USAF worked with Danish nuclear scientists to consider the clean-up options. The spilled fuel in the blackened area was heavily contaminated, raising concerns that when the ice melted in the summer, the radioactive fuel would float on the sea and subsequently contaminate the shore. The Danes thus insisted on the removal of the blackened area to avoid this possibility. The Danes also requested that the nuclear material not be left in Greenland after the cleanup operation was complete, therefore requiring Hunziker to remove the contaminated ice and wreckage to the United States for disposal. USAF personnel used graders to collect the contaminated snow and ice, which was loaded into wooden boxes at the crash site. The boxes were moved to a holding area near Thule Air Base known as the "Tank Farm". There, contaminated material was loaded into steel tanks prior to being loaded onto ships. Debris from the weapons was sent to the Pantex plant in Texas for evaluation, and the tanks were shipped to Savannah River in South Carolina. According to Hunziker, 93 percent of the contaminated material was removed from the accident site.
In 1987–88 and again in 2000, reports surfaced in the Danish press that one of the bombs had not been recovered. SAC stated at the time of the accident that all four bombs were destroyed. In 2008, the BBC published an article that was based on its examination of partly declassified documents obtained some years earlier, via the United States Freedom of Information Act. The documents appeared to confirm that within weeks of the accident, investigators realized only three of the weapons could be accounted for. One of the declassified documents—dated to January 1968—details a blackened section of ice which had refrozen with shroud lines from a weapon parachute: "Speculate something melted through the ice such as burning primary or secondary". A July 1968 report states, "An analysis by the AEC of the recovered secondary components indicates recovery of 85 percent of the uranium and 94 percent, by weight, of three secondaries. No parts of the fourth secondary have been identified".