(CNN) -- On a January night in 1961, a U.S. Air Force bomber broke in half while flying over North Carolina. From the belly of the B-52 fell two bombs -- two nuclear bombs that hit the ground near the city of Goldsboro.
A disaster worse than the devastation wrought in Hiroshima and Nagasaki could have befallen the United States that night. But it didn't, thanks to a series of fortunate missteps.
Declassified documents that the National Security Archive released this week offered new details about the incident. The blaring headline read: "Multi-Megaton Bomb Was Virtually 'Armed' When It Crashed to Earth."
Or, as Secretary of Defense Robert McNamara put it in back then, "By the slightest margin of chance, literally the failure of two wires to cross, a nuclear explosion was averted."
The Goldsboro incident
The B-52 was flying over North Carolina on January 24, 1961, when it suffered a "failure of the right wing," the report said.
As the plane broke apart, the two bombs plummeted toward the ground. The parachute opened on one; it didn't on the other.
"The impact of the aircraft breakup initiated the fuzing sequence for both bombs," the summary of the documents said.
In other words, both weapons came alarmingly close to detonating.
Weapon 1, the bomb whose parachute opened, landed intact. Fortunately, the safing pins that provided power from a generator to the weapon had been yanked -- preventing it from going off.
Weapon 2, the second bomb with the unopened parachute, landed in a free fall. The impact of the crash put it in the "armed" setting. Fortunately -- once again -- it damaged another part of the bomb needed to initiate an explosion.
The incident was first detailed last year in the book "Command and Control" by Eric Schlosser. The documents released this week provided additional chilling details.
Eight crew members were aboard the plane that night. Five survived the crash.
"I could see three or four other chutes against the glow of the wreckage," recounted the co-pilot, Maj. Richard Rardin, according to an account published by the University of North Carolina.
"I hit some trees. I had a fix on some lights and started walking."
The MK39 bombs weighed 10,000 pounds and their explosive yield was 3.8 megatons. Compare that to the bombs dropped in Hiroshima and Nagasaki: They were 0.01 and 0.02 megatons.
But Rardin didn't know then what a catastrophe had been avoided.
"My biggest difficulty getting back was the various and sundry dogs I encountered on the road."