This year marks the 50th anniversary of the Tybee Broken Arrow incident. On the 5th of February 1958 during an exercise, two U.S.A.F. planes collided resulting in the loss of a Mk-15 nuclear weapon in U.S. coastal waters off Savannah, Georgia U.S.A. |Read More|
Mk-15 TN Bomb February 4th, a B-47 Stratojet piloted by Major Howard Richardsons was leading a two-plane practice mission designed to mimic the requirements of wartime attacks on cold war targets in the Soviet Union. Typically these missions would include an aerial refuelling and a simulated "bomb drop" scored by a ground station.
The B-47's payload was an unarmed, 3,500 kg Mark 15 hydrogen bomb. The "transportation-configured" weapon had been made safe by the removal of the plutonium "pit" in the primary ensuring no full yield explosion was possible. However the bomb still contained over 180kg of conventional explosives and highly enriched Uranium (HEU), used in the weapons secondary component.
The planes had completed their mission and were returning to base in Florida, when they were spotted just after midnight by radar at Charleston Air Force Base. To add realism to SAC exercises, the bombers were often subjected to simulated attacks along the way by friendly Air Force fighters. Three F-86 Sabres were promptly scrambled to intercept the bombers 290 km north of the base.
Collison The lead F-86 locked onto one the first bomber, but failed to spot the second, the one ground radar had also missed. As he commenced his attack run, he collided with Richardson's until then unseen plane below him, ripping off both his wings. The fighter pilot managed to eject and was later recovered 35 km down wind near Garnett, S.C.
The damaged B-47 dropped it's external fuel tanks, reduced speed, descended to 6,000 meters and headed for nearby Hunter Air Force Base near Savannah. The control tower advised them that repair work had left an 45 cm drop at either end of the runway. If the B-47 landed short, the landing gear could snag, sending the contents of the bomb-bay hurtling through the cockpit and down the runway at 300-plus kph.
In light of this less than desirable outcome, the crew requested permission to jettison the bomb. Travelling at 370 kph (230 mph), Richardson's aircraft dropped the hydrogen bomb from 2,200 meters above Wassaw Sound, then landed at Hunter AFB after serveral aborted attempts.
Blast Calculator HAD the weapon detonated with it's full design yield of 3.8 megatons, the city of Savanah would have been incinerated, then smashed flat. The ensuing fallout would then have irradiated large tracts of the eastern seaboard, rendering them uninhabitable for generations.
The next day, the 2700th Explosive Ordnance Disposal Squadron were dispatched to recover the missing bomb. Over 100 U.S Navy personnel joined in the hunt for the 'broken arrow', using sonar equipment and galvanic drag-and-cable sweeps over a five square km area. Underwater divers scoured the depths, troops tromped through nearby salt marshes, and a blimp hovered over the area attempting to spot a hole or crater in the beach or swamp.
On April the 16th, the Air Force concluded its nine week search and declared that the weapon was irretrievably lost. The Air Force determined that it was prudent to leave the bomb on the sea floor rather than disturb it and risk the potential of detonation or contamination.
While the search at Tybee was still being conducted, the Air Force dispatched forces to Florence, South Carolina, where another H-bomb had been accidentally dropped by a B-47. The bomb's conventional explosives detonated on impact, sending radioactive debris across the landscape. The explosion caused extensive property damage and several injuries. Fortunately for the locals their was no nuclear detonation.
More recently, recovery efforts at Tybee have been launched amid fears that the enriched uranium could be used in an improvised gun type weapon, or a dirty bomb. In 2004, retired Air Force Colonel Derek Duke claimed to have found the resting spot of the bomb in just 3 meters of water less than two kilometers from shore. He and his partner had located the spot by trawling the area with a Geiger counter in tow. The bomb remains to this day entombed in the mud and silt at the bottom of Wassaw sound.
For bringing the B-47 and its crew back safely, Richardson was awarded the Distinguished Flying Cross. He has on his wall at home a framed copy of Atomic Energy Commission form AL-569, acknowledging his receipt on February the 4th 1958, of weapon serial number 47782.
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