Tag Archives: B28 Thermonuclear Bomb

21 January 1968

Boeing B-52G-75-BW Stratofortress 57-6471, similar to 58-0188. The numeral "3" on the vertical fin and the white cross-in-back square on the top of the fuselage identify this B-52 as a Boeing flight test aircraft. (U.S. Air Force)
Boeing B-52G-75-BW Stratofortress 57-6471, similar to 58-0188. The numeral “3” on the vertical fin and the white cross-in-black square on the top of the fuselage identify this B-52 as a Boeing flight test aircraft. (U.S. Air Force)

21 January 1968: A United States Air Force Boeing B-52G-100-BW Stratofortress, serial number 58-0188, assigned to the 380th Strategic Aerospace Wing, was flying an Airborne Nuclear Alert mission as part of Operation Chrome Dome. The bomber, call sign Hobo 28, had a crew of seven and was armed with four B28FI nuclear bombs carried in its bomb bay.

Prior to takeoff, the third pilot, Major Alfred D’Mario, had placed three foam cushions under the navigator’s seat on the lower deck of the B-52. During the flight the crew cabin became very cold and additional heat was directed into the heating ducts from an engine’s bleed air system. Due to a malfunction, the bleed air was not cooled before entering the heating system and this very hot air ignited the cushions. Very quickly a fire developed.

Boeing B-52G-100-BW Stratofortress 58-0190, the same type as Hobo 28. (U.S. Air Force)

At 12:22 p.m., Atlantic Standard Time (16:22 UTC), the aircraft commander, Captain John Haug, declared an emergency and requested an immediate landing at Thule Air Base, Greenland, which was about 90 miles (140 kilometers) to the north. The crew’s fire extinguishers were quickly depleted and the fire continued to spread. The bomber’s electrical system failed and the cabin filled with smoke. Captain Haug ordered the crew to abandon the aircraft at 16:37 UTC.

Hobo 28 passed directly over the air base and six of the seven crewmen ejected. The co-pilot, Captain Leonard Svitenko, who was temporarily in a jump seat on the lower deck rather than in an ejection seat, tried to jump from an open hatch on the lower deck. He struck his head and was killed.

Captain Haug and Major D’Mario landed on the air base, and three others were very close by. The sixth, gunner Staff Sergeant Calvin Snapp was 6 miles (9.7 kilometers) south on an ice floe, and was rescued 21 hours later.

Concentric cracks in the sea ice at the upper center of this photographic mosaic show the impact point of Hobo 28. The aircraft burned for several hours, covering the ice downwind with soot. (U.S. Air Force)

The B-52, now unmanned, continued north and then began a 180° turn to the left. It crashed onto the sea ice of North Star Bay, about 7.5 miles (12 kilometers) west of Thule.

The conventional explosives inside the four B28 bombs detonated on impact. No nuclear detonation occurred but radioactive plutonium, uranium and tritium was scattered over a wide area.

Hobo 28’s gunner, Staff Sergeant Calvin Waldrep Snapp, was rescued 21 hours later. (U.S. Air Force)

A massive cleanup effort was required. Under the circumstances, this was much more difficult than at Palomares, Spain, two years earlier.

As a result of these two nuclear accidents, referred to by the code words “Broken Arrow,” Operation Chrome Dome, which had kept armed B-52s in the air 24 hours a day since 1961, was ended.

Thule Air Base, Greenland. Mount Dundas is the flat-topped mountain just right of the center of the image. Saunders Island is in the distance. Hobo 28 crashed into North Star Bay, covered with sea ice in this photograph.
Thule Air Base, Greenland. Mount Dundas is the flat-topped mountain just right of the center of the image. Saunders Island is at the upper left. Hobo 28 crashed into North Star Bay, covered with sea ice in this photograph.

The Mark 28 was a two-stage radiation-implosion thermonuclear bomb which was designed by the Los Alamos National Laboratory and produced from January 1958 to May 1966. In 1968, it was redesignated B28. More than 4,500 were manufactured in as many as 20 variants. Explosive yield varied between 70 kilotons and 1.45 megatons. The bomb remained in service until 1991.

Three airmen position a B28Y1 1.1 megaton thermonuclear bomb for loading aboard a B-52 Stratofortress. (U.S. Air Force)

© 2019, Bryan R. Swopes

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17 January 1966

Boeing KC-135A-BN Stratotanker 58-0004 refuels Boeing B-52G-75-BW Stratofortress 57-6741. These are the same type aircraft that were involved in the 1966 Palomares Incident. (Boeing)

17 January 1966: A United States Air Force Boeing B-52G-115-BW Stratofortress, 58-0256, and its 7-man crew, along with a second B-52, were flying an Airborne Nuclear Alert patrol over the Mediterranean Sea. The bomber, call sign “Tea 16,” was armed with four Mark 28 nuclear bombs carried in its bomb bay.

At approximately 10:30 a.m., the two B-52s rendezvoused with two Boeing KC-135A-BN Stratotankers, based at Morón Air Base, Spain, for the second aerial refueling of the mission. The aircraft were at 31,000 feet (9,448 meters) off the southern coast of Spain.

Major Larry G. Messinger, a veteran of World War II, aboard as a relief pilot, was flying Tea 16 from the left seat. The aircraft commander, Captain Charles J. Wendorf, was in the right, co-pilot’s seat, while 1st Lieutenant Richard J. Rooney, the assigned co-pilot, rode in a jump seat behind them.

Major Messinger later said, “We came in behind the tanker, and we were a little bit fast, and we started to overrun him a little bit. . . .”

A boom operator’s view as a B-52 Stratofortress refuels. (John E. Considine/NASM)

B-52G 58-0256 collided with the refueling boom of “Troubadour 14” (KC-135A 61-0273). The boom penetrated the bomber’s fuselage, broke structural members and the left wing broke off. The B-52 exploded. The fully-loaded tanker, on fire, went into a steep dive. At 1,600 feet (488 meters), it also exploded.

The four crewmen aboard the tanker were killed. Three of the seven men on the B-52 ejected, and the co-pilot, who was not in an ejection seat, literally fell out of the disintegrating bomber. The navigator’s parachute did not open and he was killed. Three others were unable to escape the doomed airplane and were also killed.

Wreckage of B-52G 58-0256 at Palomares, Spain, January 1966. (Kit Talbot/The New York Times)

As the B-52 broke apart, the four nuclear bombs it carried in the bomb bay fell free. Three of them fell near the fishing village of Palomares. In two of these, the conventional explosives that “implode” the plutonium to start a chain reaction, detonated on impact, but a nuclear explosion did not occur. However, plutonium was scattered over the area. The third bomb was recovered intact, though it was slightly damaged. The retarding parachute of the fourth Mark 28 opened and it was carried offshore by the wind and fell into the Mediterranean Sea.

A massive recovery operation took place. The fourth bomb was recovered after five months. It had come to rest in an underwater canyon at a depth of 2,550 feet (777 meters).

1,400 tons of soil was packed into more than 6,000 steel drums and taken to the United States.
1,400 tons of soil was packed into more than 6,000 steel drums and taken to the United States.

558 acres (226 hectares) of land in and around Palomares was contaminated. The soil was removed and placed in steel barrels for transportation to the United States for burial at the Savannah River Plant, a nuclear reservation in South Carolina.

Three airmen position a B28Y1 1.1 megaton thermonuclear bomb for loading aboard a B-52 Stratofortress. (U.S. Air Force)
Three airmen position a B28Y1 thermonuclear bomb for loading aboard a B-52 Stratofortress. (TSgt. Boyd Belcher, U.S. Air Force)

The Mark 28 was a two-stage radiation-implosion thermonuclear bomb which was designed by the Los Alamos National Laboratory and produced from January 1958 to May 1966. In 1968, it was redesignated B28. More than 4,500 were manufactured in as many as 20 variants. Explosive yield varied between 70 kilotons and 1.45 megatons. The B28Y1 in the photograph above is a 1.1 megaton weapon. The bomb remained in service until 1991.

© 2019, Bryan R. Swopes

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