24 January 1961: “Keep 19,” a Boeing B-52G-95-BW Stratofortress, serial number 58-0187, of the 4241st Strategic Wing, was on a 24 hour airborne alert mission off the Atlantic Coast of the United States. The bomber was commanded by Major Walter S. Tulloch, U.S. Air Force, with pilots Captain Richard W. Hardin and First Lieutenant Adam C. Mattocks. Other crewmembers were Major Eugene Shelton, Radar Navigator; Captain Paul E. Brown, Navigator; First Lieutenant William H. Wilson, Electronics Warfare Officer; Major Eugene H Richards, Electronics Warfare Instructor; Technical Sergeant Francis R. Barnish, Gunner. It was armed with two Mark 39 Mod 2 thermonuclear bombs, serial number 359943 and 434909, each with an explosive yield of 3–4 megatons.
The B-52 refueled in flight from an air tanker. The tanker’s crew notified Major Tulloch that the B-52’s right wing was leaking fuel. The leak was severe and more than 5,400 gallons (37,000 pounds/17,000 kilograms) of jet fuel was lost in about two minutes. The B-52 headed for Seymour Johnson Air Force Base in North Carolina.
As they descended, the unbalanced condition made the bomber increasingly difficult to control. It may have lost a portion of a wing. The bomber went out of control and Major Tulloch ordered the crew to abandon the doomed ship. Five crewmen ejected and one climbed out through the top hatch. (Lieutenant Mattocks is believed to be the only B-52 crewmember to have ever successfully escaped through the upper hatch.)
58-0187 broke apart and exploded. Its wreckage covered a two square mile (5.2 square kilometers) area. Three crewmen, Majors Shelton and Richards, and Sergeant Barnish, were killed.
As the B-52 broke up, its two Mark 39 Mod 2 bombs fell free of the bomb bay, the first at about 9,000 feet (2,743 meters), and the second between 2,000–3,000 feet. Weapon No. 1’s (434909) parachute retarding system operated properly and it touched down essentially undamaged, penetrating the sandy soil to a depth of about 18 inches (46 centimeters). It was quickly safed by an explosive ordnance team and hauled away. Weapon No. 2, 359943, was not located until late in the afternoon of 27 January. Its parachute had not deployed and it had buried itself more than 18 feet (5.5 meters) into the ground. Large pieces of the bomb case were found beginning at a depth of 15 feet (4.5 meters). Its primary was recovered on 31 January at a depth of about 20 feet (6.1 meters).
Investigators speculated as to whether there had been a “one point” detonation of the buried bomb, but it was later determined that this had not occurred.
Recovery of the buried bomb was very difficult. After eight days, the ordnance team had recovered most of the bomb, including the 92 detonators and conventional explosive “lenses” of the “primary,” the first stage implosion section. The uranium-235/plutonium-239 “pit”—the very core of the bomb— was recovered on 29 January. The “secondary,” however, was never found.
The secondary contains the fusion fuel, but it cannot detonate without the explosion of the primary. Although the secondary remains buried, there is no danger of an explosion.
“During a B-52 airborne alert mission structural failure of the right wing resulted in two weapons separating from the aircraft during aircraft breakup at 2,000 – 10,000 feet altitude. One bomb parachute deployed and the weapon received little impact damage. The other bomb fell free and broke apart upon impact. No explosion occurred. Five of the eight crew members survived. A portion of one weapon, containing uranium, could not be recovered despite excavation in the waterlogged farmland to a depth of 50 feet. The Air Force subsequently purchased an easement requiring permission for anyone to dig there. There is no detectable radiation and no hazard in the area.”
An accident of this type, involving the loss of nuclear weapons is known by the military code name BROKEN ARROW. The accident investigators reported that, (1.) the safing pins and two arming rods had been pulled from each bomb as they fell away from the B-52; (2.) the MC-845 Bisch Generator had been operated; (3.) the MC-640 Low Voltage Thermal Battery had fired; (4.) the MC-641 High Voltage Thermal Battery had fired; (5.) the squibs for the valve mechanism for the tritium gas reservoir had not fired and the tritium remained in the reservoir; (6.) the MC-543 timer had completed its timing cycle; (7.) the MC-832 Trajectory Arming Baroswitch showed that all of the contacts had closed; (8.) the MC-788 High Voltage Safing Switch was in the “safe” position; and (9.), the MC-772 Low Voltage Arm/Safe Switch was in the “safe” position. The investigators determined that the weapon had functioned as it was expected to, having left the aircraft is a safed condition.
Components of the second weapon were significantly damaged. (1.) Its MC-543 timer had stopped after running only 12–15 seconds, and so, (2.) the MC-641 High Voltage Thermal Battery had not fired; (3.) the MC-772 Arm/Safe Switch showed ARM to visual inspection, but it was found that it was severely damaged internally, and it did not operate in an armed condition; (4.) As with the other bomb, the squibs had not fired and the tritium gas remained in the reservoir; (5.) the MC-834 Explosive Switch had been actuated, but it was broken away from the timer.
The Mark 39 was a two-stage, radiation-implosion thermonuclear bomb. It was in production from 1957–1959, with more than 700 built. It was fully fused, meaning it could be detonated by contact with the ground, as an air burst, or “lay down”— a series of parachutes would slow the bomb and it would touch down on its target before detonating. This allowed the bomber time to get clear.
The Mark 39 was considered a light weight weapon, weighing 6,500–6,750 pounds (2,950–3,060 kilograms). The bomb’s length was approximately 11 feet, 8 inches (3.556 meters), with a diameter of 2 feet, 11 inches (0.889 meters). The explosive yield of the Mark 39 was 3–4 megatons. (For reference, the 1956 nuclear weapons test at Bikini Atoll, Redwing Cherokee, had a yield of 3.8 megatons.)
The Mark 39 was withdrawn from service in the mid-1960s and replaced with the more powerful Mk 41.
© 2018, Bryan R. Swopes
