Baby-Sitting the BOMB

In 1960 as a Princeton graduate student I took a one semester course in Quantum Mechanics from Prof. Donald F. Hornig, who was also the Chairman of the Chemistry Department. I got deeply snowed under in this course, having come from a liberal arts college and possessing a weak background in the kind of mathematics required for understanding concepts such as the Schroedinger Equation.

Making matters worse, the chain-smoking Prof. Hornig was extremely high-strung, and seemed to improvise his lectures as he went along. With chalk in the right hand and an eraser in the left, he frequently changed notation in midstream, rubbing out everything on the blackboard to that point. Taking notes was nigh unto impossible. Occasionally during lectures he would light the wrong end of his Kent filter cigarettes, sending a pungent odor into the classroom.

“What in the world,” I wondered, “would make this man so nervous?” I knew that his research in physical chemistry had something to do with the study of fast chemical reactions in high-powered shock tubes. In my years in the Princeton Chemistry Department, Prof. Hornig had never said anything about his background, nor had I heard any scuttlebutt about his World War II experiences.

About thirty years later when I read Richard Rhodes 1986 Pulitzer Prize-winning book, The Making of the Atomic Bomb¹ (probably the best book ever written about the history of chemistry and physics), I finally learned what may have put Prof. Hornig so much on edge. As a 23-24 year old man in 1945, he’d had a large share of the pressure-packed hands-on responsibility for detonating history’s first nuclear bomb at the Trinity Site in New Mexico. Here for starters is the opening paragraph to Stephen Walker’s 2005 bestseller, Shockwave: Countdown to Hiroshima²:

Sunday, July 15, 1945, 9 PM. Trinity Test Site

Don Hornig stared up at the tower. The wind and rain whipped through the steel latticework. The storm that had been building throughout the day had finally erupted in all its fury. Flashes of lightning lit the San Andres mountains to the south, and the desert echoed with the growl of thunder. The tower loomed 103 feet above Hornig’s head, a network of black braces and girders reaching upward like a giant electric pylon. By now the clouds were racing so low across the sky, he could barely see the top. Which was just as well, really. He did not want to think about what was at the top.

I discovered that Hornig and his wife Lilli lived in Rhode Island, not far from my wife and me in the Boston area. In September, 2011, I decided to call him to say Hello, and his wife, Lilli, answered the phone. A Jewish refugee from Nazi Germany, Lilli was with Hornig during the Los Alamos days, and had also been a Chemistry Professor (at Brown and Trinity). They had 3 daughters and one son. I told her that I’d been very impressed at Hornig’s role in WWII by reading the Rhodes book, and she recommended the Stephen Walker book. She was happy to hear from a former student, but was sorry to say that Hornig was suffering from Alzheimer’s disease, and wasn’t able to speak on the phone or to meet us.

America’s Manhattan Project began in March, 1943, in the remote village of Los Alamos on a high New Mexico plateau. It was a crash program to beat our WWII enemies to making and deploying the first atomic bomb. The project explored the possibility of controlled chain reactions of the radioactive uranium (element number 92) isotope, U235, which existed naturally in low percentages (0.7%), and would have to be enriched in order to make enough for nuclear weapons. The other element of interest was plutonium (element number 94), which, like all trans-uranium elements (numbers 93 thru 118) is strictly man-made, and didn’t previously exist in nature. It has a fissionable isotope, Pu239, created by irradiation of the abundant uranium isotope U238, a by-product of nuclear enrichment. Both U235 and Pu239 were eventually found to have a critical mass (amount of metal that sustains a chain reaction) about the size of a softball. The uranium bomb (“Little Boy,” dropped on Hiroshima) initiated the chain reaction by taking about half the critical mass and firing it down a gun barrel at a target containing the rest of the critical mass. Not realized until April of 1944, that approach would not work for the plutonium bomb (“Fat Man,” dropped on Nagasaki) because of contamination by the strongly radioactive Pu240 isotope, which could set off the explosion prematurely.

The plutonium bomb would have to be detonated by the radical, unproven principle of implosion. That means the sphere of plutonium alloy becomes critical by at least two-fold compression from a spherical shock wave created using conventional explosives. The team decided to divide a 55 inch diameter sphere containing 5,300 pounds of high explosives Comp B (fast-reacting) and Baratol (slow-reacting) into 32 contoured segments or “lenses” in the shape of a conventional soccer ball, i.e., 12 black pentagons and 20 white hexagons, with each pentagon surrounded by five hexagons. In order to get complete explosion, the segments had to fit to tolerances less than 1 mm (requiring as an expedient the liberal use of Kleenex and scotch tape), and had to explode within 1 microsecond (one millionth of a second) of each other. This is where Don Hornig’s genius entered the picture.

A native of Milwaukee, Hornig attended Milwaukee Country Day School and then earned his undergraduate degree in chemistry at Harvard. He had completed his Ph.D. at Harvard in 1943 measuring shock waves of underwater explosions. The largest bomb he’d ever studied contained 2 tons of TNT. Now he’d be working on a nuclear explosion equivalent to 22,000 tons of TNT. He was recruited in the spring of 1945 away from his job at Woods Hole, Massachusetts by Russian-born Harvard explosives chemist Prof. George Kistiakowsky and Harvard President James B. Conant for a mysterious job somewhere in the desert out west. Why? Because, as Conant, a member of President Roosevelt’s National Defense Research Council, told him “Uncle Sam was pointing his finger at me.” Don and Lilli sold their beautiful forty-five-foot yacht Siesta, bought a used 1937 Ford coupe, and headed west with their furniture to follow a few months later. The Ford coupe survived being struck by lightning and survived the scary one-lane dirt road without guard rails up the side of a cliff to Los Alamos. (The Ford coupe was used as an ambulance several times for injured skiers including Klaus Fuchs, the German theoretical physicist who was later convicted as a Soviet spy.)

Hornig’s contribution, which he brought up while attending his first staff meeting of Manhattan Project Director J. Robert Oppenheimer was that the multiple lenses could be fired by high-voltage circuitry with sufficient simultaneity. Over the next months, Hornig designed the 400 pound X-unit of capacitors that fired the multiple detonators simultaneously. Essentially the bomb’s electric trigger, it would, at the requisite time, send a five-and-a-half-thousand-volt charge to thirty-two detonators arranged around the bomb’s sphere, like cloves stuck in an apple. Hornig invented the high voltage spark-gap switch, an essential part of the X-unit detonators, which helped to prevent accidental ignition, for example by static electricity. If anything went wrong with the X-unit, there would either be no detonation or else perhaps a minor detonation that merely wasted the precious plutonium. With a two-billion-dollar investment in the project, not to mention the outcome of WWII in the Pacific, this mustn’t have been allowed to happen.

On July 14, 1945, the scientists were not ready to test the “Gadget,” as they called the first plutonium bomb, but anyway they hoisted the four-ton beast to the top of the rickety 103 foot surplus Forest Service tower at Ground Zero of the Trinity site. On July 9th during an episode of bad weather, a test X-unit had fired spontaneously. Fortunately it was not attached to a bomb. The brilliant, but temperamental Oppenheimer, smoking 5 packs of cigarettes per day and down to 116 pounds, was beside himself, and shouted at Kistiakowsky, “What the Hell are you doing hiring an incompetent like Hornig?” Hornig discovered that a ground wire had come loose, a preventable mistake, and he was really feeling the pressure. But an okay weather forecast and the tense political situation at the Potsdam Conference, where President Truman was negotiating an end to WWII with Churchill and Stalin, determined that the test must be run on Monday morning, July 16, at 3:00 AM. Secretly, Stalin was well aware of the American atomic program and had a secret program of his own. The implications of a successful test of the US A-bomb at this moment for establishing the post-war free West vs Soviet East world order were immense.

On that same day, disaster struck again. A test was conducted on a “Chinese copy” of the bomb, i.e., an identical bomb with everything in place except the fissionable plutonium “pit”. The simultaneity of the implosion was measured magnetically. It was not good, and the report to Oppenheimer was that the Trinity test was likely to fail. A pallor of gloom fell over the project. Many bets were placed, wagering on the power of the explosion and whether there would be any explosion at all. Others, such as the Italian physicist Enrico Fermi, predicted that the explosion would ignite the earth’s atmosphere and possibly lead to mass extinction. Oppenheimer consoled himself by reading Hindu poetry in Sanskrit. Expectations for a successful firing on July 16 couldn’t have been lower, and now Hornig was seriously in the doghouse. Oppenheimer was worried about everything, but sabotage was high on his list. Thus he ordered Hornig up the tower to look after the Gadget.

When Hornig climbed the tower on July 15th at 9 PM he also had some work to do, installing the best X-unit in place of one that had been used for practice. As described by Walker,

At the top of the tower, a simple corrugated tin shack rested on a square wooden platform. It was a flimsy, cheaply made structure, obviously not designed to last. It was not much bigger than a garden shed. One of its walls was open to the elements. Hornig stepped off the ladder beside it, pausing by the entrance. A huge, dimly discernible shape crouched inside. There was a bare sixty-watt bulb hanging from the roof. Hornig switched it on and peered inside. Hulking on a cradle was a metallic-gray, bloated, four-ton drum of steel [aluminum alloy], and it took up almost every inch of space in the shack. Even by day it would have looked ominous, but it looked especially so now with the wind whipping the tin walls, and the dim bulb swaying from the ceiling, and the lightning and thunder edging nearer³. A fantastic complex of cables sprouted from its sides like a spillage of guts or arteries, as if it were somehow not inert at all but actually organic, a growing, living, autonomous embryo, awaiting the moment of its birth.

The Arming Party headed by Bainbridge arrived at 11 PM and when they were finished, Hornig was alone with the Gadget, waiting for a phone call to come down the ladder. The bomb was now fully armed. Walker continues,

Don Hornig now found himself sitting all alone on top of a tower in the middle of a violent electrical storm, next to an atomic bomb. There were clearly ample opportunities here for a little philosophical speculation, but Hornig chose not to indulge. Instead, he started to read a book. It was a cheap paperback thriller called Desert Island Decameron. It was not, he remembers, a very good book. Of course, it was hard to read in the [swaying,] dim sixty-watt light. Plus his concentration skills were not quite up to their usual levels. After all, Hornig knew perhaps better than anyone that a well-placed lightning strike could perform precisely the same function as one of his X-units. lt could quite easily set off the detonators, in turn igniting the 5,300 pounds of Comp B and Baratol high explosive surrounding the nuclear core of the bomb. Even if the bomb failed to go nuclear, the high explosive alone made it the biggest conventional weapon of the war.

Hornig got the phone call around midnight to come down from the tower, but after one sleepless 24 hours, another sleepless night was just beginning. The thunderstorm and high winds got worse, and Oppenheimer postponed the shot from 0300 till 0530, when the storm should have passed and it was still dark. While the Arming Party stayed at Ground Zero till 0500 to guard against sabotage, Hornig drove a jeep to the command bunker S-10,000 located at 5.7 miles south of Ground Zero where the actual firing would take place. His job was to watch the countdown on various instrument panels, and be ready to open the knife-blade switch nicknamed the “chicken switch” that would stop the countdown in case there was any sign of trouble in his judgement. As described by Rhodes,

At thirty seconds before T = 0 four red lights flashed on the console in front of him and a voltmeter needle flipped from left to right under its round glass cover to register the full charging of the X-unit. Farrell noticed that “Dr. Oppenheimer, on whom had rested a very heavy burden, grew tenser as the last seconds ticked off. He scarcely breathed. He held on to a post to steady himself. For the last few seconds, he stared directly ahead.”

As described by Rhodes, the last decisive inaction was Hornig’s,

Now the sequence of events was all controlled by the automatic timer except that I had the knife switch which could stop the test at any moment up until the actual firing. I don’t think I have ever been keyed up as I was during those final seconds. I kept telling myself “the least flicker of that needle and you have to act.” It kept on coming down to zero. I kept saying, “Your reaction time is about half a second and you can’t relax for even a fraction of a second.” My eyes were glued on the dial and my hand was on the switch. I could hear the timer counting … three . . . two . . . one. The needle fell to zero.

 

Time: 0529:45. The firing circuit closed; the X-unit discharged; the detonators at thirty-two detonation points simultaneously fired; they ignited the outer lens shells of Composition B; the detonation waves separately bulged, encountered inclusions of Baratol, slowed, curved, turned inside out, merged to a common inward-driving sphere; the spherical detonation wave crossed into the second shell of solid fast Composition B and accelerated; hit the wall of dense uranium tamper and became a shock wave and squeezed, liquefying, moving through; hit the nickel plating of the plutonium core and squeezed, the small sphere shrinking, collapsing into itself, becoming an eyeball; the shock wave reaching the tiny initiator at the center and swirling through its designed irregularities to mix its beryllium and polonium; polonium alphas kicking neutrons free from scant atoms of beryllium: one, two, seven, nine, hardly more neutrons drilling into the surrounding plutonium to start the chain reaction. Then fission multiplying its prodigious energy release through eighty generations in millionths of a second, tens of millions of degrees, millions of pounds of pressure. Before the radiation leaked away, conditions within the eyeball briefly resembled the state of the universe moments after its first primordial explosion.

At the base camp some 10 miles south of Ground Zero, Enrico Fermi had torn up little bits of paper, and when the shock wave arrived about 40 seconds after the blast, he released the paper pieces and measured how far they were carried. With a slide rule he calculated the power of the blast at 10,000 tons of TNT, five times the power of the bombs that had destroyed Dresden, Germany. His estimate was low by a factor of two.

Brighter than daylight, the exploding Gadget reached a temperature of 60 million degrees centigrade, ten thousand times hotter than the surface of the sun, instantly melting the aluminum alloy that encased the bomb, all the cables and switches, the folding chair that Hornig had been sitting on, the car battery that generated the high voltages for the detonator, heck, the 103 foot steel tower was vaporized without a trace. As written by Walker,

Don Hornig had rushed out of the control bunker the instant the count hit zero. As the flash flooded the desert, he tore up the stairs then looked up. The huge, expanding cloud boiled up into the skies almost directly above him like a mountain growing out of the earth. But the most astonishing spectacle was the colors, a glorious riot of luminescent pinks and blues and greens spilling out of the cloud before themselves unfolding whole spectra of new colors, until the sky became one vast and dazzling fireworks display. It was the most beautiful sight Hornig had ever seen.

Lilli Hornig had driven with some friends near the top of 10,600 ft. Sandia Peak just northeast of Albuquerque, 180 miles away from the Trinity site. Expecting the blast at 3 AM, they had almost given up when the sky lit up at 5:30 AM — a dazzling performance beyond description.

Of course, mixed with the elation of having solved a difficult problem in physics, chemistry, engineering, metallurgy, etc., was the repulsion experienced by many of the scientists knowing that atomic power would likely be used for evil as well as beneficial purposes. This was exacerbated by the fact that the war against Hitler, their principal enemy, was already finished. Oppenheimer’s recollections were reported by Rhodes as follows:

We waited until the blast had passed, walked out of the shelter and then it was extremely solemn. We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent. I remembered the line from the Hindu scripture, the Bhagavad-Gita: Vishnu is trying to persuade the Prince that he should do his duty and to impress him he takes on his multi-armed form and says, “Now I am become Death, the destroyer of worlds.”

Following World War II, Don Hornig served on the faculty of Brown University from 1946-1957 as a professor and dean. From 1957 he taught at Princeton University and served as the chair of the chemistry department. At the same time, he also served on the President’s Science Advisory Committee for both President Dwight Eisenhower and President John F. Kennedy. In 1963, Kennedy appointed Hornig as a presidential science advisor, an office he held from 1964-1969, before returning to Brown University as the school’s president where he helped to establish Brown’s medical school. In 1976 he moved to Harvard’s School of Public Health, where he chaired the Department of Environmental Health until his retirement in 1990. Hornig was a member of the National Academy of Sciences, the American Academy of Arts and Sciences, and the American Philosophical Society. He was a recipient of both a Guggenheim Fellowship and a Fulbright Fellowship.

Jim Sudmeier Revere, MA first draft Sept. 19, 2011

P.S. One night after dinner in the Princeton Graduate College in 1960, about 20 of us graduate students were treated to an informal chat in a student lounge with J. Robert Oppenheimer, Director of the neighboring Institute for Advanced Studies. A sad man who had been persecuted by Senator McCarthy and his followers, and had been stripped of his security clearance, it was fascinating to meet the man and hear his stories.

P.P.S. In 2013 I made another phone call to Lilli Hornig. She said that Don had passed away. We exchanged several conversations about getting together for a visit, but she died in 2017 before we were able to arrange it. She referred me to Prof. Hornig’s 8 minute oral history as an 85 year old man in 2005 about his role in the successful Trinity test: http://www.npr.org/templates/story/story.php?storyId=4757424

[1]  Rhodes, Richard. The Making of the Atomic Bomb. New York: Simon & Schuster, 1986.
[2]   Walker, Stephen. Shockwave: Countdown to Hiroshima. New York: Harper Collins Publishers, 2005.
[3] Walker’s description of the wind and rain during Hornig’s stay in the tower (9PM thru midnight) despite the peak thunderstorm starting at 2 AM is confirmed by the quotation from Hornig after climbing the tower,”By then there was a violent thunder and lightning storm.” in the book by Reed, Bruce C. The History and Science of the Manhattan Project. New York: Springer, 2013.

Comments:

Among several people I sent this story to was my second cousin Steve Wangsness, a retired US State Dept agent.  Here is the gist of my email:

I was the first person in my immediate family that went to college, but I did have a first cousin, once removed, named Roald Wangsness, a graduate student in physics at the U. of Minnesota who was sent off to Los Alamos in 1943 to work on the Atomic Bomb. Later he studied at Stanford and helped his boss win the Nobel Prize in Nuclear Magnetic Resonance (NMR), my field of research during my career. I don’t have any stories about what Roald did at Los Alamos, mostly because he died out in Tucson, Arizona before I could meet him a few years ago. But I had a physical chemistry teacher in graduate school who played a very interesting, dangerous, and suspenseful role in developing the bomb, which I have written up here in six pages, which I think might interest you.

Steve’s response:
Hey, Jim. I finally got around to reading this, which was quite interesting. I guess my father must have known and worked with Dr. Hornig, since he worked on the triggering device, too. Though it might have been only on the plutonium bomb? I don’t know. I know relatively little about Mom and Dad’s work in Los Alamos. What I do know is this.

Dad was recruited by his physics professor and left for New Mexico in late March or early April, 1944 (not 1943), once he received his B.A. I asked him why they were recruiting punk physicists who only had a B.A. and he said at that time, there weren’t that many physicists! Not like now. This also helped him get a full professorship at the Univ. of Maryland when he was 31 or 32. Mom came down in July, 1944 and they got married the day she arrived (or maybe the day after). DId you know they only knew each other for a few weeks when Dad left for New Mexico and despite the short time, they were already engaged? Worked out pretty well. They honeymooned at Bandelier Natl. Monument, and that’s where their ashes were scattered.

Anyway, I know Dad worked on the triggering device. He once blew himself across the room after accidentally touching some high-voltage piece of equipment with a screwdriver. I really don’t know much more about his work. While Mom and Dad both met Oppenheimer and some of the other mucky-mucks, generally they didn’t run in the same circles. Somehow, my mother had enough interaction with Edward Teller to develop a big and lifelong distaste for him. Most of the Los Alamos stories I have came from Mom. She worked in the medical section doing blood tests and checking radiation badges, etc. She once made a cake when they had another young couple over and Dad complimented her by saying it was just like he liked cake, nice and heavy. She never really forgave him for that. She once saved all her meat ration coupons for a long time so she could get a big ham for Christmas (or something) but they changed the regulations just before she went to get it and you could no longer get more than X amount of meat at a time, regardless of how many coupons you had.

My favorite story is the time Enrico Fermi (yes, that Fermi) gave her a ride somewhere. She made him (a Nobel Prize winner!) stop the car so she could pick wildflowers. They stopped at a diner somewhere and Fermi demonstrated the principle of conservation of motion with a playing card and a nickel placed on top of a water glass. I mean, Enrico Fermi!  Dad claimed he never met David Greenglass, Julius Rosenberg’s brother-in-law. I think he was the only known spy that I ever asked him about.  Neither attended or saw the test, though they did get a small vial of Trinitite, the glassy residue of the plutonium bomb test, which I still have. They were all happy about the use of the bomb on Japan; no one at the time as far as Mom recalled had any reservations. According to Mom, VJ Day was the only time she’d ever seen my father drunk.  Don’t know if you’ve ever seen this, but you can look at Mom and Dad’s Los Alamos ID cards (as well as those of others, like spies Klaus Fuchs and Theodore Hall) here:  https://www.lanl.gov/about/history-innovation/badges.php