Here, revealed for the first time, is how nine scientists were caught 20 miles from ground zero when the biggest H-bomb of all time went off. This is their chilling story. Saturday Evening Post, July 1957
. . . by Dr. John C. Clark as told by Robert Cahn
May, 1956: Fireball over Bikini. This is what America's first H-bomb blast looked like from a plane 12,000 feet up and 50 miles away.
When we locked open the main firing switch in the control room before leaving to arm the H-bomb that February day at Bikini in 1954, I had no feeling that this one would be any different from the more than forty other nuclear test shots in which I had participated. Since it was a thermonuclear bomb of a relatively large predicted yield which we were testing, we had tried to figure out in advance all the possibilities of danger and to make allowances for all eventualities. But this is not easy when one is concerned with a device which produces an explosive force roughly equivalent to 15,000,000 tons of TNT --- 1000 times more powerful than the Hiroshima atom bomb.
The energy released by the thermonuclear blast -- which we call the "yield" -- could not be pre-determined with absolute accuracy. Nor could we tell beforehand exactly how extensive the air-wave and tidal-wave effects would be or the precise amount and distribution of the "fallout"-- the radioactive particles from the nuclear cloud which drop back to earth. In the business of testing nuclear devices there are always a few unknowns.The temperature was in the high eighties, the sky was clear and there was just a slight breeze blowing as we got into the helicopters for the flight to the shot island approximately twenty miles northwest, at the other end of Bikini atoll. It was a perfect day for the end of February--far different from the weather at some places Stateside. All our extensive preparations for this first shot in Operation Castle had come off on schedule and we contemplated no trouble ahead. Little did we realize that within eighteen hours we would become unsolicited human guinea pigs during the strangest and most hazardous effects ever experienced from an American nuclear test.
| After clearing the coconut palms through which our landing strip had been cut, I looked down at our sturdy control blockhouse. It certainly seemed out of place among the palms and pandanuses on our tiny tear-drop-shaped island. Coral sand covered most of the roof--sand which the radiation experts said would help protect anybody inside the building from stray fallout radiation. |  This is the sand covered bunker in which the author and eight others were trapped by the deadly fallout in Operation Castle. They were rescued by helicopter. |
The structure had also been sealed to withstand up to at least a five-foot tidal wave and built of reinforced concrete to resist the overpressure and underpressure effects expected from the blast. It certainly looked secure enough even to satisfy those who had argued that we would be safer if the firing were controlled from a greater distance. But inasmuch as our control island, Enyu, was the most distant spot on the atoll from ground zero, to go farther would have necessitated firing from a ship. And we wanted to avoid the more complicated ship-controlled firing if at all possible.
It was now shortly after noon and as our Marine helicopter pilot headed north over the atoll, I could see the last few supply ships pulling away from Enyu. The operational plan called for all ships to be safely out to sea by the time we armed the gadget. We hoped to have the arming completed and be back at the control island in time for the helicopters to return to their mother ships before dark.
As we headed across the lagoon to the first of our instrument stations, the string of islands and reefs which comprise Bikini atoll looked like so many beads on a necklace. The largest islands are one to two miles long and at their widest are less than 800 yards across. Others are no more than reefs or sandspits. In a few minutes we dropped down onto one of the small islands. While Herb Grier, an electrical engineer from Boston, checked on some of the recording instruments, I locked open a part of the circuitry in a blast-proof bunker. The Commander of the firing party must lock open all the switches in the firing circuits with padlocks and keep the only key. It's not that we don't trust others. But in the business of arming a thermonuclear bomb, you must be absolutcly certain that no circuits are closed at the time of arming.
| About two o'clock, after making a few more stops to check on instruments and to lock open switches, we arrived at the shot site. With me were Grier and Barney O'Keefe, both of the Boston firm of Edgerton, Germeshausen and Grier, electrical contractors to the Atomic Energy Commission. Already there, having flown up in another helicopter, was Dr. Gaelen Felt, one of the top young scientists from Los Alamos. |  Inside the blockhouse: Here, only 20 miles from ground zero, Dr. Felt (Right) and an assistant man test devices. Radiation from the 1954 Blast penetrated this room. |
Felt, Grier and O'Keefe had specific duties concerned with the numerous optical and electronic experiments which are always co-ordinated in the test of a nuclear device. My job was to check on everything at the shot site, and then, when all was in order, to arm the bomb.
We were almost finished with the checking when Gaelen discovered helium, used in optical experiments, leaking from one of the key setups. Some rapid calculations disclosed that by shot time the next morning there would not be sufficient pressure left in the tanks to carry out the experiment. I radioed the information to Dr. Alvin C. Graves, scientific deputy to the task-force commander, who was aboard the command ship. Without this experiment, the test would not be held.
We soon discovered that we could not fix the leaks in the short time left. But we came up with another solution to the problem. If we delayed the arming procedure for seven hours and opened the valves at the last possible moment, there would still be enough helium for the experiment. We did not desire to return after dark because our island landing mat had no lights. However, it was either set back the arming or postpone the test and Doctor Graves gave us the go-ahead for our emergeney plan.
We sat around until dark taking it easy while the whirly-bird pilots went off to a nearby construction site and scrounged some food that had been left there by the workmen. The temperature, which varies less than ten degrees night and day, was still in the eighties. Shortly before eleven P.M. we opened the valves of the helium tanks. I then requested permission from the command ship to arm the bomb. Before the final connections are made, a check must be made to determine that no other personnel are in or near the shot island. We are pretty darn sure the bomb won't go off when we arm it, but with the complex circuitry involved there is always the one chance in a million that something might go wrong.
Barney and Herb accompanied me to the artificial sandspit which was ground zero, This "island" had been dredged up out of the coral sand so that it could be in the most advantageous position for the shot. As a safety precaution, we always have someone else along to check every action of the person arming the device just to make doubly certain that each step is done correctly. Much of the work in an atomic test can be done by automation, but for all the experimental bomb tests so far we have done the arming by hand.
All went according to plan, however, and I made the final connections which armed thc bomb. We quickly got into the helicopters and headed back, retracing our path to close the switches I had lockcd open earlier in the day. The pilots could easily follow the white-coral shoreline and we got back to Enyu about midnight. The men who had been checking things at the control point took our places in the helicopters, which then scooted off to join their ships, already headed away from the shot site.
There were nine of us remaining in the blockhouse. In addition to Doctor Felt, O'Keefe, Grier and myself, there were Dr. Harold Stewart, a scientist from the Naval Research Laboratory; Lt. Douglas Cochrane, a radio expert; John L. Sanderson, of Holmes & Narver, Los Angeles contractors who did the construction work • and two radio technicians, Airman First Class Gerald Scarpino and Master Sergeant Alton Greene.
We made our last-minute checkouts of circuits and then waited for the final weather reports from the command ship. Around three A.M.-- zero hour was scheduled for shortly before daybreak--the scientific director radioed, "We have just had the weather briefing and we agreed to continue. So go ahead and start the count-down."
Herb Grier, who was making the time announcements, waited for the tone from WWV, thc world-wide standard-time station. "It is now minus two hours," announced Grier at the beep of the signal. Almost 100 miles away, on small islands in the atolls of Rongelap, Rongerik and Utirik, technicians from an American military weather group checked their watches and recording devices. At other points on the ocean, personnel on ship instrumentation stations synchronized their time settings. And in the air, pilots and navigators coordinated with our announcement to make certain they would be at their correct position at shot time. Other aircraft had already completed search flights in the area and had seen no stray ships. Apparently, as we found out later, they somehow failed to spot the little Japanese trawler Fukuryu Maru--the Fortunate Dragon--fishing about seventy miles off our shot island.
At minus one hour we started our final preparations. I told John Sanderson to button up the generators in a nearby concrete bunker and to secure the control building. After closing the doors to the structure housing the generators, Sanderson climbed a ladder outside our blockhouse to put metal plates and gaskets over the air-conditioning vents. He then entered the blockhouse and sealed the submarine hatch which had been installed as our only door and which was completely watertight and blastproof.
At H hour minus fifteen minutes I told Grier to push the button on the automatic sequence timer. Contrary to popular belief, we don't push a button to set off the bomb. Everything is done electrically by the sequence timer, although up until the last second I can pull a switch to stop the bomb from going off. Also there are "no-go" devices built into the circuitry which automatically prevent the detonation-- should any of the primary experiments not be ready to function properly. There are hundreds of experiments conducted during most nuclear detonations, but we usually limit those which can lock out a detonation to four or five. However, some of these four or five circuits are closed so late that even at the last second we are not sure that a no-go device won't halt the test.
Those last few scconds in the control room are always quite tense. We keep watching the control panel, where lights flash from red to green to show when experiments and circuits are rcady to operate. Somc remote-controlled cameras near the bomb are not turned on until between minus three quarters of a second and minus a half second. We would rather not have to rely on such delicate timing, but these ultra-high-speed cameras work at a rate of over l,000,000 frames a second and require split-second control.
The purpose of nuclear detonations is always to obtain experimental data, and it would be a waste of money and months of scientific effort if the bomb went off and the recording equipment was not in complete readiness.
After the sequence timer had been started, we all gathered in the control room for a final briefing. I requested that all who were not needed in the control room should stand in the hall. I told them that although we expected no difficulty, there would he a ground shock shortly afer the bomb went off. This would be followed by the air shock wave, which, at twenty miles' distance, would probably do no great damage. Finally, there was the possibility of a tidal wave sweeping over the building. If it came, it was due at about H plus seven minutes. I told them I had agreed with Doctor Graves that, inasmuch as we had no observation winldows, we would wait until H plus fifteen minutes before "unbuttoning" the building, to make absolutely sure we were not under water.
At H minus ten minutes, Grier, O'Keefe and Lieutenant Cochrane manned posts at the control panel. Hal Stewart was in a nearby room where he had his spectrographic instruments, and I stayed in the center of the control room.
"At the next tone it will be H minus one minute," announced Grier a few minutes later.
"Thirty seconds," announced Grier. "Fifteen...." All exccpt two of the lights were green. "Ten . . . nine . . . eight . . . seven ... six ... five...." All was absolutely quiet except for the soft whining of the sequence timer. "Four . . . three . . . two . . . one . . . Zero."
