The Tybee Bomb: When the USAF Dropped a Nuclear Weapon on Savannah GA

In 1958, a US Air Force bomber on a training mission collided with an American fighter plane over Savannah GA. Before the crippled bomber could make an emergency landing, it had to jettison the thermonuclear weapon it was carrying–so it dropped the H-bomb somewhere near Tybee Island. And there the bomb remains today, almost 60 years later.

Boeing B-47E
B-47 nuclear bomber                                                                                                              photo from US Air Force

In the 1950’s, at the height of the Cold War, the US Air Force was prepared for nuclear war with the Soviet Union at any moment. To train for Armageddon, bombers from the Strategic Air Command routinely flew practice missions to simulate dropping bombs on Russian cities. These missions involved taking off from bases in the US, flying eight or ten hours (with mid-air refueling stops along the way, making mock bomb runs over an American city and “dropping” an electronic bomb simulator signal (which would score them on their accuracy). As part of their training, the bombers would often be “intercepted” and “attacked” by American fighter planes, who were practicing their own wartime missions.

At 4pm on February 4, 1958, two SAC B-47 bombers took off from the Air Force runway in Homestead FL. Their mission was to fly to Louisiana, refueling over the Gulf of Mexico, then go north to the Canadian border before turning south again to drop an electronic practice bomb in Virginia before returning to Florida. Each bomber had a crew of three. Commanding the mission was Major Howard Richardson, who had over 1,000 hours flying experience in the B-47 and who often trained new pilots.

Before taking off, Richardson had signed a copy of Form AL-569 from the US Atomic Energy Commission, acknowledging that he had been given custody of, and assumed responsibility for, one of America’s deadliest weapons–a Mark 15 Mod 0 thermonuclear hydrogen bomb, serial number 47782. The bomb was 11 feet 7 inches long and weighed 7,600 pounds, which was about one-fourth the weight of its predecessor the Mark 14–the Mark 15 was intended as a “lightweight” aerial bomb. Inside, it contained a fission atomic bomb similar to the one dropped on Nagasaki, and a cylinder made of “highly-enriched uranium” that contained tritium and deuterium, two forms of hydrogen. When dropped on a Soviet city, the heat and pressure from the fission explosion would cause the hydrogen isotopes to fuse, releasing energy and also free neutrons, which would in turn produce fission in the uranium. In total, the bomb produced about 4 megatons of energy. Within a radius of two miles, destruction would be total.

But because this was only a practice mission, the Mark 15 in the B-47’s bomb bay was not a live weapon–it had been “safed” by removing the plutonium core, about the size of a softball, that triggered the nuclear explosion and replacing it with a dummy core made of lead. This was known as “transportation configuration”. Scrawled across the top of Richardson’s Form AL-569 was the word “simulated”. The dummy weapon was not intended to be dropped during these practice missions, but was there to give the airplane a realistic weight and handling characteristics.

Mk15
Mark 15 nuclear bomb, with a yield of about 4 megatons         photo from US Air Force

The mission went smoothly. The two B-47s made their bomb runs over Reston VA and beamed their electronic bomb simulator at the ground, then turned home for Florida. By midnight they were flying over the city of Savannah GA. And then things went wrong.

At the nearby Air Force Base in Charleston SC, three fighter pilots were on alert, with their F-86L Sabre interceptors standing by, fully fueled. This operation was also a training mission for them: in a real war, their job would be to take off as quickly as possible and shoot down any Soviet bombers. Just a few minutes after midnight the “scramble” signal rang out–radar had picked up the incoming B-47 flight (though for some reason only one of the two bombers was detected) and the three F-86s were sent to intercept it.

The lead fighter plane was piloted by Lieutenant Clarence Stewart. About fifteen minutes after taking off, Stewart was in “intercept” position, below and a few miles behind the bomber flight, and had locked on with his F-86’s onboard radar. At this time, air radar was relatively primitive, and Stewart’s fighter locked on to the B-47 that was furthest away from him. Because the base radar had reported only one incoming bomber, Stewart did not know that there was a second B-47 in front of him. And because it was dark out and he was carefully watching his radar screen, he didn’t see it until the very last second. As he just happened to glance up from his radar screen, Stewart later reported, his canopy was “filled with airplane”. Instinctively he threw his fighter into a hard right turn, but it was too late. The F-86’s left wing collided with the right wing of the B-47. The fighter’s wing was completely sheared off, and the resulting fuel explosion broke off the right wing as well. Stewart immediately bailed out, and his parachute carried him all the way to South Carolina, where he landed in a swamp near a ranger station.

Major Richardson’s B-47, meanwhile, was seriously damaged. The right wingtip and gas tank were gone, and the outboard right engine had been twisted upwards, pushing the big bomber into a bank to the left. To balance the wings, Richardson shut off the damaged engine and dropped the fuel tank on the left wing, then quickly did a “landing check”, reducing his speed and lowering his landing gear to see if the crippled plane was still capable of reaching the ground. He then headed for the nearest landing field, Hunter Army Base in Savannah.

But on the way there, Richardson was informed that some work had recently been done on the landing field, and that the edge of the runway was sticking up about 16 inches in the air. If the crippled B-47 landed short, the landing gear would catch on this obstruction, possibly flipping the plane over and causing a fire. And while the “safed” Mark 15 bomb had no active core and could not initiate a nuclear explosion, it still carried the 400 pounds of conventional explosives which were used to implode the plutonium core and set off the bomb. Those conventional explosives would be detonated if there were a fire, destroying the plane and killing all three men aboard. Or, if the plane came to a sudden stop from the impact, the heavy bomb might rip itself loose and its momentum would carry it right through the plane and out the nose, squishing the cockpit and its crew. Major Richardson decided that the only safe thing to do was to get rid of the bomb before he landed. He circled around the airfield and headed out towards the water, radioing to SAC HQ that he intended to jettison his nuclear weapon. As he passed over Tybee Island in Savannah at about 7,000 feet, he opened the bomb bay and dropped the Mark 15. It fell away into the night. Official Air Force reports say that SAC HQ had radioed permission to jettison the bomb, but Richardson now admits that he had already released the Mark 15, on his own authority, before SAC had given the OK.

With his crippled plane now almost four tons lighter, Richardson was able to circle back to Hunter Field and land the B-47. Racing in at some 80mph over the normal landing speed, he deployed the landing chute while still in the air, held the right wingtip as high as he could to avoid dragging the damaged engine, and made it safely to the ground. His coolness under pressure had saved the plane and the three crew members, and he would soon receive the Distinguished Flying Cross for his actions that night.

But there was still the matter of the lost nuke.

P1230303
The mouth of the Savannah River, off Tybee Island. The Mark-15 bomb is somewhere around here.

The next morning, the Navy and Air Force began a search for the errant Mark 15. All they knew was that the bomb had been dropped near the southern tip of Tybee Island, and could be anywhere within a several-mile radius of that point. Most likely, the searchers assumed, the bomb’s momentum would have carried it a couple miles offshore into Wassaw Sound, where the water was between 6 and 40 feet deep. Since Richardson had not reported an explosion when the Mark 15 hit the water, it was most likely that the conventional explosives had not detonated on impact, and that the bomb had tunneled through the water and hit the bottom of the Sound intact, nose-first, and buried itself several yards into the mud. (It was also possible that the bomb had landed on one of the nearby islands, where it would have disappeared into the gooey muck of the area’s many tidal salt marshes.) Experts from Los Alamos concluded that the impact would have torn loose many of the bomb’s internal components, and the heavy uranium “secondary core” would likely have pushed its way out through the nose of the bomb.

About 100 military technicians from the Navy and Air Force swept three square miles of land and water with metal detectors, geiger counters, sonar, and dredging cables. They found nothing. In April, after two months of searching, the Air Force declared the Mark 15 to be “irretrievably lost” and called off the recovery effort. And so the bomb still remains out there, somewhere.

Since that time, the “Tybee Bomb” has become something of a local legend. A few local residents have made a hobby out of searching for it. Conspiracy theories have appeared declaring that the bomb was actually armed with a live core and could go off any day now, destroying Savannah in a thermonuclear blast. This conspiracy theory is often prompted by a confusion about the bomb: the Mark 15 nuclear weapon was actually produced in two different versions, the Mod 0 and the Mod 2. The Mod 0 had a removable plutonium core that could be replaced by an inert lead sphere to “safe” the nuke and make it incapable of producing a fission reaction. Later, the internal layout of the Mark 15 was altered to produce the Mod 2: in this configuration, the plutonium core could no longer be removed, and instead the bomb was “safed” with a series of electrical switches. The Mod 2 change was not introduced until the summer of 1958, however, months after the Tybee Bomb was lost, but there are still occasional newspaper stories claiming that Richardson’s B-47 was carrying a Mod 2 with a live core. This speculation was fueled in 1966, when Assistant Defense Secretary Jack Howard testified during a secret session before a Congressional Committee about the US nuclear arsenal. In his classified testimony, Howard stated that there had been up to that time four accidents that had resulted in the loss of a complete fully-armed nuclear weapon. The Tybee Island bomb was included in that list.

From the contemporary documents, we know that the Mark 15 loaded onto Richardson’s B-47 was a Mod 0, and that it had no nuclear core. Assistant Secretary Howard was simply wrong in his testimony, as he later acknowledged. But when the testimony was declassified, the conspiracy theories flew thick and fast. In 2000, Georgia Congressman Jack Kingston asked the Air Force to determine once and for all whether the Tybee Bomb had actually been armed, whether it could now be found with modern technology, and whether it presented any danger to the area and should be removed. The Air Force spent a year studying the issue.

In 2001, the Pentagon issued their report. There was, they concluded, no possibility of a nuclear explosion. The bomb contained no plutonium core. The secondary stage of the bomb did contain weapons-grade uranium (the amount remains classified), but this was in a configuration in which it was impossible to form a critical mass and set off a nuclear reaction. The enriched uranium did, however, present a potential hazard if it were released into the waters of Wassaw Sound. Uranium is a toxic heavy metal, and, although uranium metal is very dense and would not drift far from the bomb, it could present a poisoning hazard to marine life in the immediate vicinity. The radiation hazard was judged to be very low, since uranium has a long half-life and is not very active radiologically, and even if the bomb casing had broken open and exposed the uranium to the sea, the leaching of metal into the water would be very slow and the heavy uranium particles would not travel more than a few feet from the bomb. Repeated surveys of the area showed no “hot spots” of abnormally-high radiation. The biggest potential danger with the bomb, the Air Force concluded, was the 400 pounds of conventional explosive it still contained. If the bomb were to be disturbed in some way, these explosives could potentially be triggered to go off and produce dangerous underwater shock waves to a distance of several hundred feet. Small boats or divers in the water could be at serious risk.

The Air Force then considered possible ways to find the bomb. Underwater sonar or cameras would not work, since it was presumed that the bomb was buried by at least 10-15 feet of sediment. Magnetometers, designed to detect underwater metal, would also not be able to penetrate that far into the muck. The only workable option would be low-frequency audio-scanners, which beam powerful sound waves like radar into the bottom and sense objects by the varying returns that are received. But, the study concluded, the potential search area consisted of several square miles, which could only be covered at the rate of one square mile every 12 days. And even then, the relatively small size of the bomb would make it very difficult to locate (and would also produce a lot of “false positives” from other objects in the seafloor, each of which would have to be dug out and inspected). Further, even if they managed to find the bomb, actually removing it would be a hazardous process due to the degraded conventional explosives still present.

In the end, the Air Force concluded that finding and removing the bomb would be difficult and dangerous, whereas if the bomb were simply allowed to stay where it is, sealed over by mud and muck, it does not present any significant environmental or safety risk. The Pentagon did agree that it would reconsider the matter if the bomb was ever accidentally discovered by someone.

Until then, the Tybee Bomb will remain where it is–wherever that might be.

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4 thoughts on “The Tybee Bomb: When the USAF Dropped a Nuclear Weapon on Savannah GA”

  1. The now-defunct Florence (SC) Air & Missile Museum had a neat exhibit about the Mars Bluff nuke. The Wiki entry for that incident says the Florence County Museum now has an exhibit that includes some bomb fragments.

  2. Hi Lenny,

    A year late, but did get to read your Tybee article. Was the USN back-up radioman on the search team and, to the extent I was in on things, can confirm you got it right.

    1. Thanks for dropping by. 🙂

      I heard they found a radioactive “hot spot” a while ago and thought it might be the missing bomb, but it turned out to be a natural deposit of rock. The bomb is probably buried so deep by now that it’ll never be found.

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