The bomber crashed onto sea ice in North Star Bay,[a] Greenland, causing the conventional explosives aboard to detonate and the nuclear payload to rupture and disperse, resulting in radioactive contamination of the area.

USAF Strategic Air Command "Chrome Dome" operations were discontinued immediately after the accident, which highlighted the safety and political risks of the missions.

In 1960, the 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.

[6] 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.

[4][7][b] The monitoring mission started when the designated aircraft reached a waypoint at 75°0′N 67°30′W / 75.000°N 67.500°W / 75.000; -67.500 in Baffin Bay and entered a figure-eight holding pattern above the air base at an altitude of 35,000 feet (11,000 m).

[6] 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 ($1.19 billion as of 2025) could be saved annually.

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.

[8] On 21 January 1968, a B-52G Stratofortress, serial number 58-0188, with the callsign "HOBO 28"[9] from the 380th Strategic Bomb Wing at Plattsburgh Air Force Base, New York was assigned the "Hard Head" mission over Thule and nearby Baffin Bay.

[12] 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.

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.

[16] 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.

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.

[11] 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,[11] but he survived by wrapping himself in his parachute.

[11][24] 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.

[21] American and Danish officials immediately launched "Project Crested Ice" (informally known as "Dr. Freezelove"[d][35]), a clean-up operation to remove the debris and contain environmental damage.

[44] The Danes also requested that the nuclear material not be left in Greenland after the cleanup operation was complete, therefore requiring General Hunziker to remove the contaminated ice and wreckage to the United States for disposal.

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.

He explained the logic behind the decision to abandon the search: "There was disappointment in what you might call a failure to return all of the components ... it would be very difficult for anyone else to recover classified pieces if we couldn't find them".

One document from July 1968 reads, "Fact that this operation includes search for object or missing weapon part is to be treated as Confidential NOFORN",[52] meaning it was not to be disclosed to non-US nationals.

Diagrams and notes included in the declassified documents make clear it was not possible to search the entire area where crash debris had spread.

[61] By the time the operation concluded, 700 specialized personnel from both countries and more than 70 United States government agencies had worked for nine months to clean-up the site,[35] often without adequate protective clothing or decontamination measures.

[63] The accident, which occurred two years after the Palomares crash, signaled the immediate end of the airborne alert program, which had become untenable because of the political and operational risks involved.

[64] Scott Sagan, a political science academic and anti-nuclear writer, postulated that if the HOBO 28 monitoring aircraft had crashed into the BMEWS early warning array instead of Baffin Bay, it would have presented NORAD with a scenario (radio link to "Hard Head" aircraft and BMEWS both dead, no nuclear detonation detected) that also matched that of a surprise conventional missile attack on Thule, leaving the unreliable submarine telecommunications cable between Thule and the US mainland as the only source of information to the contrary.

[74] The Lawrence Livermore National Laboratory developed the "Susan Test", which uses a special projectile whose design simulates an aircraft accident by squeezing and nipping explosive material between its metal surfaces.

Denmark's nuclear-free zone policy originated in 1957, when the coalition government decided in the lead-up to the Paris NATO summit not to stockpile nuclear weapons on its soil in peacetime.

When the two-volume work was published on 17 January 1997[87] it confirmed that the nuclear-armed flights over Greenland were recurrent, but that the United States had acted in good faith.

security agreement: he was not asked about, nor did he mention, the official Danish nuclear policy when meeting with the United States ambassador in 1957 to discuss Thule Air Base.

[82][89] The DUPI report also revealed details of Project Iceworm, a hitherto secret United States Army plan to store up to 600 nuclear missiles under the Greenland ice cap.

The documents revealed that USAF personnel involved in the clean-up were not subsequently monitored for health problems, despite the likelihood of greater exposure to radiation than the Danes.

However, the plutonium contamination of surface soil at Narsaarsuk could constitute a small risk to humans visiting the location if radioactive particles are resuspended in the air so that they might be inhaled".