“Aircraft 53-1876A Has Lost A Device”

PrintPrintEmailEmailOn the afternoon of March 11, 1958, the Gregg sisters—Helen, six, and Frances, nine—and their cousin Ella Davies, nine, were in the playhouse their father had built for them in the woods behind their house in Mars Bluff, South Carolina. About four o’clock they tired of the playhouse and moved 200 feet to the side yard. This kept them from becoming the first Americans killed by a nuclear weapon released on U.S. territory. U.S. Air Force B-47E medium bomber serial number 53-1876A dropped its nuclear weapon in the woods behind the Greggs’ house at 4:19 P.M. The high-explosive trigger in the bomb blew up on contact with the ground, leaving a crater 50 feet across and 35 feet deep and injuring the three girls. All that remained of the playhouse were a few twisted shards of the corrugated metal that had been its roof.

At 8:00 that morning Capt. Earl Koehler, pilot; Capt. Charles Woodruff, co-pilot; Capt. Bruce Kulka, navigator/bombardier; and crew chief Sgt. Robert Screptock had arrived at Hunter Air Force Base just outside Savannah, Georgia, to fly their B-47 in Operation Snow Flurry that afternoon. Snow Flurry was not routine training but rather part of a “Unit Simulated Combat Mission and Special [i.e., nuclear] Weapons Exercise.” Briefings for the mission had begun ten days before takeoff, and two generals had appeared to emphasize the exercise’s importance. Aircraft 53-1876A, accompanied by three other B-47s from the 375th Bombardment Squadron, was to carry a nuclear weapon to Bruntingthorpe Air Base, England, conducting a midair refueling en route off the east coast of Canada. Before landing, the crew was to make a practice bomb run over England, transmitting an electronic signal to simulate the bomb release. Computers on the ground were to determine the accuracy of the “drop” and award points accordingly. Had the mission been completed, the crew would have had a tense, exhausting 18-hour day.


The bomb

Nuclear weapons then, as now, contained a high-explosive trigger to compress a uranium/plutonium core to a critical mass and initiate the chain reaction of a nuclear explosion. Perhaps the single greatest trick in nuclear-weapons design is to focus the immense force of the trigger explosion onto the core with precisely the proper geometry, strength, and timing to compress it to the exact degree required by the laws of physics to start a chain reaction, rather than simply blow the bomb apart. There are two types of high explosives that could be used in the trigger. One could be set off by concussion, such as a bullet or contact with the ground; the other—the type the military today invariably insists upon—could take great physical abuse without going off. Unfortunately, the triggers used in nuclear weapons in 1958 contained the former.


The plane

The six-engine B-47 was the first modern jet bomber. The initial production model came out in March 1950; at more than 600 miles an hour, it was faster than any operational jet fighter in the world. It had a three-man crew with room for one passenger and was capable—barely—of crossing the Atlantic without refueling. On takeoff a fully loaded B-47 was virtually a flying gas tank, being just over 52 percent fuel by weight. But it could not dump its internal fuel tanks in an emergency, as could civilian airliners, and it wasn’t structurally strong enough to land safely with a large fuel load. When a fully fueled B-47 left the ground on takeoff, the choice was either to fly for several hours in order to burn off fuel or to crash. Nuclear weapons could add another 5,000 to 20,000 pounds, making the aircraft even harder to fly. Perhaps feeling some guilt over its failure to provide the B-47 with adequate safety features, the Air Force stipulated that on takeoff and landing the crew should be able to drop its nuclear weapon(s) promptly in an emergency, at least marginally improving the pilot’s ability to control the aircraft.

Nuclear weapons were held in a B-47 by two systems: a complicated but reliable pneumatically powered catch that could be operated by the crew and a manually inserted steel locking pin. With the locking pin in place, it was impossible to drop the weapon. With the pin out, the crew could jettison the weapon almost immediately. By regulation, the locking pin was to be out for landing and takeoff.