Tag Archives: Nuclear Weapons Accident

5 February 1958

Boeing B-47E-55-BE Stratojet 51-2394, similar in appearance to Ivory Two. Photographed 7 April 1956. (U.S. Air Force)

On the night of 4–5 February 1958, two Boeing B-47 Stratojet bombers from MacDill Air Force Base, Florida, were flying a simulated bombing mission. The second bomber, B-47B-50-BW serial number 51-2349, was under the command of Major Howard Richardson, USAF, with co-pilot 1st Lieutenant Bob Lagerstrom and radar navigator Captain Leland Woolard. Their call sign was “Ivory Two.”

Aircrew of B-47, left to right, Major Howard Richardson, Bob Lagerstrom and Leland Woolard. (U.S. Air Force)

Carried in the bomb bay of Ivory Two was a 7,600-pound (3,448 kilogram) Mark 15 Mod. 0 two-stage radiation-implosion thermonuclear bomb, serial number 47782. The bomb had been developed by the Los Alamos National Laboratory. The Mod. 0 had an explosive yield of 1.69 megatons.

Bomb, Thermonuclear, Mark 15.
Bomb, Thermonuclear, Mark 15. (Nuclear Weapons Archive)

After completing their simulated bombing mission, the B-47s were returning to their base in Florida.

On the same night pilots of South Carolina Air National Guard were on alert at Charleston Air Force Base with their North American Aviation F-86L Sabre interceptors. The fighters were fully armed with twenty-four 2.75-inch (70 mm) rockets. At 00:09 a.m., the pilots were alerted for a training interception of the southbound B-47s. Within five minutes three F-86Ls were airborne and climbing, with air defense radar sites directing them. In one of the F-86Ls, 52-10108, an upgraded F-86D Sabre, was 1st Lieutenant Clarence A. Stewart, call sign, “Pug Gold Two.”

The flight of interceptors came in behind the bombers at about 35,000 feet (10,668 meters). Tracking their targets with radar, they closed on the lead B-47, Ivory One, from behind. Ivory Two was about 1 mile (1.6 kilometers) in trail of Ivory One, but the airborne radars of the Sabres did not detect it, nor did the ground-based radar controllers.

This North American Aviation F-86L-60-NA Sabre, 53-1047, of the 444th Fighter Interceptor Squadron, Charleston, South Carolina, is similar to 1st Lieutenant Clarence A. Stewart's F-86L-50-NA 52-10108, destroyed in the collision with the B-47, 5 February 1958. (U.S. Air Force)
This North American Aviation F-86L-60-NA Sabre, 53-1047, of the 444th Fighter Interceptor Squadron, Charleston Air Force Base, South Carolina, is similar to 1st Lieutenant Clarence A. Stewart’s F-86L-50-NA 52-10108, which was destroyed in the collision with the B-47, 5 February 1958. (U.S. Air Force)

At 00:33:30, 5 February, Lieutenant Stewart’s fighter collided with the right wing of Major Richardson’s bomber. The Sabre lost both wings. Lieutenant Stewart fired his ejection seat. His descent from the stratosphere took twenty-two minutes and his hands were frostbitten from the cold. He spent five weeks in an Air Force hospital. Pug Gold Two crashed in a farm field about 10 miles (16 kilometers) east of Sylvania, Georgia.

Damage to the right wing and aft fuselage of B-47B 51-2349. (U.S. Air Force)

The B-47 was heavily damaged. The outboard engine had been dislodged from its mount on the wing and hung at about a 45° angle. The wing’s main spar was broken, the aileron was damaged, and the airplane and its crew were in immediate jeopardy. The damage to the flight controls made it difficult to fly. If the number six engine fell free, the loss of its weight would upset the airplane’s delicate balance and cause it to go out of control, or the  damaged wing might itself fail.

Damage to the right wing of B-47B 51-2349. (U.S. Air Force)

Major Richardson didn’t think they could make it back to MacDill, and the nearest suitable airfield, Hunter Air Force Base, Savannah, Georgia, advised that the main runway was under repair. A crash on landing was a likely outcome.

Damage to the aft fuselage and vertical fin of B-47B 51-2349. (U.S. Air Force)

With this in mind, Richardson flew Ivory Two out over Wassaw Sound, and at an altitude of 7,200 feet (2,195 meters) the hydrogen bomb was jettisoned. It landed in about 40 feet (12 meters) of water near Tybee Island. No explosion occurred.

The B-47 safely landed at Hunter AFB, but was so badly damaged that it never flew again. Major Richardson was awarded the Distinguished Flying Cross for his handling of the incident.

The missing Mark 15 has never been found and is considered to be “irretrievably lost.” It is known as “The Tybee Bomb.”

Clarence Arville Stewart was born 17 October 1934 at Drew, Mississippi. He was the son of John B. Stewart and Cleta R. Stewart. Stewart soloed a airplane for the first time at the age of 13 years. By the time he was 15, he had enlisted in the Mississippi National Guard. His actual age was discovered as his unit was preparing to deploy during the Korean War, and he was sent home.

After studying at the Mississippi Delta Community College at Moorehead, Mississippi, Stewart enlisted in the U.S. Air Force as an aviation cadet. On graduation from flight training, he was commissioned as a second lieutenant, United States Air Force Reserve, in 1956.

In 1958, Lieutenant Stewart married Miss Patricia Ann Hudson of Beaufort, South Carolina. They would have three children. Mrs. Stewart passed away in 2010.

This Republic F-105D Thunderchief, 61-0165, is the sister ship of 61-0160, the aircraft flown by Captain Clarence A. Stewart on 2 June 1966. (John E. Considine/NASM-91A14248)

Eight years after the mid-air collision with the B-47, Captain Stewart was in Thailand, assigned to the 421st Tactical Fighter Squadron, 388th Tactical Fighter Wing, based at Korat Royal Thai Air Base. Flying a strike mission on 2 June 1966, the the engine of his Republic F-105D-20-RE Thunderchief, 61-0160, exploded. Stewart ejected from his airplane for the second time in his career. The fighter bomber went down approximately 55 miles (89 kilometers) northeast of Korat. Captain Stewart was picked up by helicopter.

Captain Clarence A. Stewart

Stewart flew over 100 combat missions over North Vietnam. He was awarded the Silver Star for his actions of 1 August 1966: “While leading a flight of F-105s against an oil storage tank fabrication in North Viet Nam, Capt. Stewart was caught in a deadly cross fire from several SA-2 missile sites. He was turned back from the target three separate times by a total of eight SA-2 surface-to-air missiles, yet he persisted in his attack until his communication equipment was seriously damaged by an exploding missile and his flight had only recover fuel remaining. In the midst of the SAM barrage, Captain Stewart demonstrated his calm and courageous leadership by directing his wingman’s escape from an uprushing missile.” Major Stewart was awarded the Distinguished Flying Cross for another flight in which he destroyed two anti-aircraft sites.

The following year, Major Stewart was assigned as chief of the Aerial Review Control Team based at Eglin Air Force Base. The unit was responsible for controlling air shows, other than those flown by The Thunderbirds. (A junior member of the team was 1st Lieutenant Steve Ritchie, future fighter ace.)

Lieutenant Colonel Stewart retired from the Air Force in 1977. He died at Fort Walton Beach, Florida, 15 January 2015.

Boeing B-47B-50-BW 51-2348, sister ship of Ivory Two. (U.S. Air Force)

Designed by Boeing, the Stratojet was a high-subsonic-speed strategic bomber and reconnaissance aircraft, in service from 1951 until 1977. The B-47 could fly higher and faster than jet fighters of the time, and it was also highly maneuverable. The B-47 was flown by a two pilots in a tandem cockpit. A navigator/bombardier was at a station in the nose.

The Boeing B-47B Stratojet was the first full-production model. The B-47B is 106 feet, 10 inches (32.563 meters) long with a wingspan of 116 feet, 0 inches(35.357 meters), and an overall height of 27 feet, 11 inches (8.509 meters). The wings are shoulder-mounted with the leading edges swept aft to 36° 37′. Their angle of incidence  is 2° 45′ and there is no dihedral. (The wings are very flexible, showing marked anhedral on the ground and flexing upward when in flight.) The B-47B has an empty weight of 78,102 pounds (35,426 kilograms), and a maximum takeoff weight of 185,000 pounds (83,915 kilograms). The maximum in-flight weight (after air refueling) was 221,000 pounds (100,244 kilograms).

From 1953 to 1957, the B-47B fleet underwent an extensive modification program which brought them up to the B-47E configuration.

A Boeing B-47B-40-BW Stratojet 51-2212 of the 306th Bombardment Wing (Medium) rolling out after landing at MacDill AFB, Florida. This airplane is similar to B-47B 51-2349, Ivory Two. (U.S. Air Force)

The B-47B was originally powered by six General Electric J47-GE-11 turbojet engines in four nacelles mounted on pylons below the wings. All B-47Bs after serial number 51-2046 were equipped with J47-GE-23 engines. The airplanes built with the -11 engines were retroffitted with the -23s. Under the modification and upgrade program, the -23s were replaced by the J47-GE-25. This engine has a 12-stage axial-flow compressor, eight combustion chambers, and single-stage turbine. The J47-GE-25 is rated at 5,970 pounds of static thrust at Sea Level, at 7,950 r.p.m. and 1,250 °F. (677 °C.) turbine outlet temperature (TOT). (7,200 pounds of thrust with water injection). It has a maximum diameter of 3 feet, 1 inch (0.940 meters) and length of 12 feet, 0 inches (3.658 meters) and weighs 2,653 pounds (1,203 kilograms).

The B-47B was also equipped with solid-fuel rocket engines (JATO) located in the aft fuselage. These produced a maximum 33,000 pounds of thrust (146.8 kilonewtons) for 14 seconds.

The B-47B Stratojet had a cruise speed of 433 knots (498 miles per hour/802 kilometers per hour), and maximum speed of 528 knots (608 miles per hour/978 kilometers per hour) at 16,300 feet (4,968 meters). The service ceiling was 42,100 feet (10,333 meters) and combat ceiling 40,800 feet (12,436 meters).

The combat radius of the B-47B was 1,704 nautical miles (1,961 statute miles/3,156 kilometers with a 10,000 pound (4,536 kilograms) bomb load. Two jettisonable underwing fuel tanks could carry 1,780 gallons (6,738 liters) each. The maximum ferry range was 3,861 nautical miles (4,443 statute miles (7,151 kilometers).

For defense the B-47B was armed with two Browning AN-M3 .50-caliber machine guns in a remotely-operated tail turret, with 600 rounds of ammunition per gun. The co-pilot acted as the gunner using an optical sight. The machine guns were replaced by two M24A1 20 mm autocannons and radar control.

The maximum bomb load of the B-47B was 18,000 pounds (8,165 kilograms). The B-47 could carry two 7,600 pound (3,447 kilogram) Mark 15 two-stage radiation implosion thermonuclear bombs, each with an explosive yield of 3.8 megatons, or a single 10,670 pound (4,808 kilogram) B-41 three-stage, 25 megaton bomb.

Beginning in 1953, the B-47B fleet underwent an extensive modification program which brought them up to the B-47E configuration.

A total of 2,032 B-47s were built by a consortium of aircraft manufacturers: Boeing Airplane Company, Wichita, Kansas; Douglas Aircraft Company, Tulsa, Oklahoma; Lockheed Aircraft Company, Marietta, Georgia. 399 of these were B-47Bs.

The Stratojet is one of the most influential aircraft designs of all time and its legacy can be seen in almost every jet airliner built since the 1950s: the swept wing with engines suspended below and ahead on pylons. The B-47 served the United States Air Force from 1951 to 1977. From the first flight of the Boeing XB-47 Stratojet prototype, 17 December 1947, to the final flight of B-47E 52-166, was 38 years, 6 months, 1 day.

© 2019, Bryan R. Swopes

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24 January 1961

Boeing B-52G-75-BW Stratofortress 57-6471, similar to 58-0187. 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 58-0187. 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)

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 thermonuclear bombs, 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 less than three minutes. The B-52 headed for Seymour Johnson Air Force Base in North Carolina.

Boeing B-52G-95-BW Stratofortress 58-0190, the same type as Keep 19. (U.S. Air Force)

As they descended, the unbalanced condition made the bomber increasingly difficult to control. 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 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 bombs fell free of the bomb bay. One buried itself more than 180 feet (55 meters) deep. The other’s parachute retarding system operated properly and it touched down essentially undamaged. It was quickly safed by an explosive ordnance team and hauled away.

One of teh two Mk 39 bombs that fell from the B-52 as it broke up near Goldsboro, South Carolina, 24 January 1961.
One of the two Mk 39 bombs that fell from the B-52 as it broke up near Goldsboro, North Carolina, 24 January 1961. The parachute retarding  system had deployed, allowing the bomb to touch down with minimal damage.

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.

Most of the Mark 39 bomb was uncovered from an excavation at the farm field near Goldsboro, North Carolina. (U.S. Air Force)

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. Though official statements were that there was no danger that either of the bombs could have exploded, others indicate that five of the six steps (or six of seven) required for a thermonuclear detonation did occur. Only the aircraft commander’s arming switch had not been activated.

Bomb, Mark 39Y1 Mod 2, P/N 300611-00, serial number 4215, at the National Museum of the United States Air Force. Behind it is a Convair B-36 Peacemaker ten-engine strategic bomber. (U.S. Air Force)

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.)

Fireball from detonation of TX-15 weapon, Operation Redwing Cherokee, 21 May 1956. (Nuclear Weapons Archive)

The Mark 39 was withdrawn from service in the mid-1960s and replaced with the more powerful Mk 41.

© 2018, Bryan R. Swopes

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