A Few Words About This Picture
At first glance you might think this picture is an image dreamed up for some 1950s science-fiction movie: Attack of the Giant Thermos Bottles . But it’s real enough. One can only imagine what those who saw this top-secret behemoth thought as it rumbled on the rail lines along the Mississippi in the spring of 1945, making its way from the foundries of the Babcock & Wilcox Company, in Barberton, Ohio, to the north end of White Sands Proving Grounds, at Alamogorclo, New Mexico. At 214 tons it was the heaviest thing ever shipped by rail.
As its destination suggests, it was built at the order of the Manhattan Engineer District (MED) of the Army Corps of Engineers, the group responsible for building and using the first atomic bombs—the Manhattan Project. The plan was to explode the first plutonium bomb, the one that would eventually be tested in the New Mexico desert, inside this container. Unsurprisingly, the vessel was known as Jumbo. The story of its creation, like the object itself, is astonishing.
MED had two primary tasks. The first was to accumulate significant amounts of fissionable materials; the second was to design and fabricate the explosive devices that would make use of the material—atomic bombs. Of the two tasks, the first required by far the most money and effort.
In 1943 there were two means of amassing large amounts of fissionable materials. One was to separate and collect the different isotopes of uranium. The common isotope, with an atomic weight of 238, is not fissionable; the much rarer isotope (1 atom in 140), atomic weight 235, is. Since isotopes are chemically identical, their separation had to be effected by mechanical means. Most of the facilities at Oak Ridge, Tennessee, were developed to pursue this task, and they devoured almost a billion dollars in the process.
The second method was the manufacture of a new element: plutonium. Uranium 238, though itself not fissionable, could be transformed into fissionable plutonium 239 in a nuclear reactor. The facilities to accomplish this were built at Hanford, Washington, in 1943 and 1944. That installation cost upward of three-quarters of a billion dollars.
All this activity was coordinated by the head of the Manhattan Project, Army Corps of Engineers Gen. Leslie R. Groves. At the time of his appointment, Groves had been in charge of all Army construction within the United States, and he had built an enviable reputation for getting things done with dispatch. Once Groves saw the solution to a problem, he would pursue it with ruthless tenacity. His ferocious style inspired two responses: He was loved and admired by some and hated and feared by most. There were no neutrals.
As construction began on the factories, reactors, and chemical laboratories at Oak Ridge and Hanford, Groves undertook to build and staff a new laboratory at Los Alamos, New Mexico. This facility would be used for the design and fabrication of atomic bombs under the direction of J. Robert Oppenheimer.
The basic physics of an atomic bomb is exceedingly simple: Once a critical mass of fissionable material is assembled, a self-sustaining fission process is set off, releasing enormous amounts of energy until the critical mass itself gets blown apart. The reaction is astonishingly fast. The entire process is over in a tiny fraction of a microsecond, so the critical mass must be assembled in an exceptionally short time. In 1943 the most obvious solution was to assemble a bomb by using a cannon to fire one subcritical piece of fissionable material into another.
A second idea was to use ordinary high explosives to implode a subcritical hollow shell of fissionable material so that it merged as a solid critical assembly. But the placement of the explosives and the timing of their detonation would have to be extraordinarily accurate. Scientists soon determined that they could relax the timing requirements somewhat by imploding a subcritical solid sphere rather than a hollow shell, but the problem remained daunting.
On the basis of their initial research, Oppenheimer and his associates became so sure the gun assembly would work that they never tested it in a full-scale device. The uranium 235 gun-assembly bomb that was dropped on Hiroshima justified their confidence in that technique. But when that first uranium bomb was assembled, in July 1945, it contained all the fissionable uranium that Oak Ridge had produced at the time. There wouldn’t be enough material for a second such bomb until January 1946.
The implosion technique, on the other hand—which ultimately relied on plutonium and was used for the Nagasaki bomb—resisted solution at first. As Oppenheimer noted in a memo written in February 1944, “The implosion gadget [bomb] must be tested in a range where the energy release is comparable with that contemplated for final use. Quite apart from general arguments which indicate the necessity for complete tests on so radical an innovation, this test is required because of the incompleteness of our knowledge.”
At the time, General Groves was adamant in his opposition to such a test, and the reasons are not hard to fathom. The reactors and chemical plants at Hanford were under construction, yet many of the processes they would carry out were untried, and the experts who reported to Groves were unsure of how productive these plants would be. Further, no one could say how much plutonium would be needed for each bomb.
Groves’s earlier experience had included testifying before sometimes hostile congressional committees that demanded justification for the expenditures he authorized. He envisioned that if the war ended before an atomic bomb had been successfully developed, he would have to face a Congress that had largely been kept in the dark about his hugely expensive project and would have to testify that he had authorized an implosion test that not only had failed but in the process had used up the world’s entire supply of plutonium—three-quarters of a billion dollars’ worth—with no more to come for a very long time. It was his worst nightmare.
In March 1944, a month after Oppenheimer first indicated that a test of an implosion bomb would be necessary, Groves relented somewhat when the physicist promised that there would be no test without a reliable system for recovering the plutonium in the event that the implosion did not result in a nuclear chain reaction. (There would be no recovery if the bomb worked.) Three techniques were considered: covering the bomb with a large quantity of sand, detonating the bomb in a big tank of water, and exploding the bomb inside a huge steel vessel. The sand and water methods were quickly ruled out as impracticable. For the third method, Oppenheimer estimated that a steel sphere weighing as much as eighty tons would be required to withstand the blast of the approximately five thousand pounds of high explosives used for the implosion. The details of design and construction awaited further calculation and testing.
When scale models based on a spherical design tested poorly, Robert W. Henderson, the supervisor of design at Los Alamos, obtained Oppenheimer’s permission to recruit Roy W. Carlson, Henderson’s old professor of civil engineering at Berkeley. Carlson saw the problem as one of dynamics, not strength of materials. He and Henderson proposed a design in which a central cylinder was wrapped with layers of tensioned steel and capped at either end with hemispherical bells. After the container was positioned properly, it would be girdled with a layer of concrete, cast in place. When the explosive lenses were detonated, the force of the explosion would be dissipated in the acceleration of the tensioned walls of the massive container and the pulverization of the concrete girdle. Tests of scale models—so-called Jumbinos—showed that the design was feasible.
In July 1944, about the time that Carlson and Henderson had worked out what appeared to be a successful design for Jumbo, the implosion program took on an urgent new status. Experiments with the first reactor-produced plutonium revealed that assembly by gun, the method perfectly suitable for the uranium being produced at Oak Ridge, would be far too slow for plutonium. The only conceivable assembly technique for plutonium was implosion.
For everyone connected with the project—especially Groves—this was a crisis of major proportions. Hanford was close to completion. Implosion was far from perfected. Groves faced the prospect of having invested in a huge, expensive industrial complex whose product was unusable. Not surprisingly, the implosion program became the number-one priority at Los Alamos. The laboratory was completely reorganized, and the number of personnel increased dramatically.
Carlson and Henderson began looking for a steel company willing to meet the challenge of fabricating Jumbo, which, for security purposes, was now officially referred to as a “hydraulic accumulator.” Plans called for a cylinder with an inside diameter of 10 feet and a length of 15 feet. The hemispherical end caps brought the overall interior length to 25 feet. The cylinder and end caps would be fashioned from six-inch plate steel, and tensioned sheet steel would be wrapped around the cylinder, bringing its final wall thickness to 16 inches. The outside dimensions would be a diameter of 12 feet 8 inches and a length of 28 feet, and the device would weigh 214 tons. Access would be provided by a manway in one of the hemispheres. Unsurprisingly, most of the companies approached balked. But by the beginning of August 1944 Babcock & Wilcox, an operation with great experience in the construction of high-pressure containment systems, had accepted the assignment.
Construction of Jumbo was well under way in October, when Alamogordo was approved as the site for the test. Apparently it was only then that Manhattan Project officials began investigating the problem of shipping Jumbo from Babcock & Wilcox’s shops, in Barberton, Ohio, to New Mexico. The job of transporting Jumbo was given to the Eichleay Corporation of Pittsburgh, experts in heavy moving. The logistics for the transport of all military equipment was being handled by the War Department’s Office of the Chief of Transportation. Responsibility for getting particularly ungainly or extraordinarily large and heavy loads from one place to another lay with Caot. A. Whildin. Jr.
Whildin’s job was so unusual that toward the end of 1944 Liberty magazine scheduled an article reviewing some of his most bizarre assignments. Manhattan Project security people learned to their horror that one example in the article was going to be Whildin’s struggle to find a route for Jumbo. The device itself would be described as “we can’t tell you what,” but the article would claim that “this thing is so enormous that it seems only sensible to first make sure it could be shipped across country before it was built. … [Captain Whildin] has worked on it like mad for six months now, and so far, the theoretical thing is stuck on a railroad somewhere in Canada. Can’t figure out a way to get it back down into the states and out to the coast.” It is a measure of Groves’s power that by the time the article appeared, in March 1945, all references to Jumbo were gone.
By that time Whildin had figured it all out. Groves, who had been unwilling to reveal the true destination of the shipment until it was absolutely necessary, represented it as Los Angeles, the end point of the Atchison, Topeka and Santa Fe Railroad, which had a siding about thirty miles from Alamogordo. The route chosen ran from Barberton, Ohio, to Griffith, Indiana, via the Erie Railway; from Griffith to Joliet, Illinois, via the Elgin, Joliet and Eastern Railway; and then along the Mississippi to New Orleans and on to Los Angeles on the Atchison, Topeka and Santa Fe. In order to accomplish this, three trestles had to be rebuilt, and Whildin ordered the train not to exceed thirty miles an hour. It was only after Jumbo had left for New Orleans in mid-April that Groves allowed the railroad to know the true destination. The trip took three weeks.
When Jumbo arrived at the siding, it was offloaded onto a specially built sixty-four-wheel (in an eight-by-eight arrangement) trailer and dragged across the desert by four tractors. The original scheme called for two tractors pulling and two pushing Jumbo, but photographs of the operation show three tractors pulling and one considerably behind, to make sure Jumbo couldn’t run away on downhill portions of the thirty-mile journey to its final destination, half a mile from ground zero. Once there, it was hoisted upright into a steel framework and rested on a concrete pad poured around it.
The reason Jumbo was deposited half a mile from ground zero was that a de facto decision had already been made not to use it. Throughout the winter and spring of 1945 those responsible for the instrumentation at the test site grew increasingly restive as they realized the degree to which placing the bomb inside Jumbo would affect measurements. They estimated that if the nuclear explosion was big enough to vaporize Jumbo completely, the fireball would grow twice as large as planned, and the now-radioactive 214 tons of iron would condense and fall to the ground a quarter of a mile away from the detonation site. K. T. Bainbridge, director of the test, later reported that a two-track plan had been followed until March, accommodating either use of Jumbo or a “naked” test. After March “it was no longer possible to make test plans that did not interfere [with each other].”
The fact that Jumbo was shipped signifies that when it left Ohio no official decision had been made; that didn’t happen until May 15. By then Groves was no longer insisting on a scheme for the recovery of the plutonium. For one thing, plutonium was now being produced in quantity at Hanford; for another, the general was impressed by the optimism at Los Alamos about progress on implosion techniques.
Though the surrounding steel framework was left a twisted mass and the concrete base on which it sat was pulverized by the Trinity detonation, Jumbo was left unscathed and unmoved. There is no question that Jumbo was an embarrassment to Groves. The cost of fabricating it and moving it out to the site had been twelve million dollars—0.6 percent of a project that itself represented 1 percent of the 1945 gross national product.
After the war Capt. C. E. Bush, the officer in charge of the Trinity site, assured Groves that he had hidden the sixty-four-wheel trailer for a while, that the wheels and tires had eventually been sold as surplus, and that the body had been cut up into unrecognizable pieces and sold for scrap.
Then in April 1946, surely on Groves’s orders, 1st Lt. Richard A. Blackburn oversaw what was termed a test of Jumbo. Eight 500-pound bombs were lowered to its bottom and detonated. To the lieutenant’s surprise, both the end bells blew off, and a chunk of Jumbo estimated to weigh more than 15 tons landed 750 feet from the detonation site.
Carlson and Henderson were furious, and Babcock & Wilcox was sorely disappointed. Jumbo had been designed to withstand an explosion of much greater force—but with the charge suspended at the center of the cavity. Groves was undoubtedly relieved. Subsequent attempts to bury, burn, or otherwise dismember the damaged remains, a cylinder weighing about 180 tons, were for naught.
Later, in-the 1960s, when the town of Socorro, New Mexico, built a museum, White Sands Proving Grounds offered Jumbo as a donation. The town was eager to obtain the.prize, but there was no way to transport it across the bridge that spanned the Rio Grande and connected Socorro with the Trinity site. Today Jumbo rests at Alamogordo a few yards from the Ground Zero monument, a serene rusting hulk and a silent, virtually anonymous tribute to the resolute will of Leslie R. Groves.