Isegoria

As the work got under way, General Groves explains (in Now It Can Be Told: The Story of the Manhattan Project), some amazing rumors began to circulate through Santa Fe, some thirty miles away:

Typical of these was that old stand-by that we were building a home for pregnant WAC’s.

[…]

After a number of Navy officers had been assigned to the project, and were seen on the streets of Santa Fe, rumors burgeoned about the new type of submarine that was being perfected on the Hill, as Los Alamos came to be known locally. Although the nearest navigable body of water was many hundreds of miles away, this rumor sounded entirely plausible to a number of people.

[…]

Colonel G. R. Tyler, the military commander at Los Alamos, once boarded a train at the railway stop nearest Santa Fe, and in the club car sat next to a man in civilian clothes who had gotten on at the same station. The stranger at once began a one-sided, rapid-fire conversation. It was obvious that he had failed to note the fact that Tyler had boarded the train at the same time that he had for, finally, he lowered his voice and said, “If we can find a secluded spot, I can tell you something which, I think, will interest you.”

Both men walked to the vestibule of the car, and stood while the man related his story. “You’d never believe the strange things that are happening on a certain mountain about fifty miles from Santa Fe. They’re doing some work that is very secret and the place is surrounded by belts of tall wire fencing. In order to keep intruders out, between these belts of fences they keep ferocious packs of wild African dogs. Besides, there are thousands of heavily armed soldier guards, and I can tell you that a number of people have been killed by the guards, or torn to pieces by the animals. It’s a frightful thing! However, I suppose that in wartime these things have to be.” He then told of other strange happenings on the Hill, none of which were true, and concluded with, “Of course, I happen to be one of the very few residents of Santa Fe who know what they are doing up there, but I do hope that you won’t ask me any questions. You see, I’ve given my word of honor that I will not divulge their secrets.”

By this time the train was approaching Tyler’s station, and as the stranger followed him to the platform he said, “Colonel, I forgot to ask you, but where are you stationed, and what sort of an assignment have you?” The officer replied, “I am stationed at Los Alamos, and I command the military personnel there.” The horrified and now extremely red-faced stranger said, “I hope that you’ll forget everything that I’ve told you. I don’t really know what’s going on at the Hill. I merely repeated some of the things that I’ve heard.”

The general principles governing control of information were simple, General Groves explains (in Now It Can Be Told: The Story of the Manhattan Project):

First, nothing should be published that would in any way disclose vital information. Second, nothing should be published that might attract attention to any phase of the project. Third, it was particularly important to keep such matters out of any magazine or newspaper that was likely to be read by an enemy agent or by anyone whose knowledge of scientific progress would enable him to guess what was going on.

[…]

We were only too aware that the piecing together of bits of published information is a prime source of knowledge to every intelligence organization.

It was in order to prevent speculative articles as well as the publicizing of any of our efforts that the press and radio had been asked to avoid the use of certain words, such as “atomic energy.” Certain decoy words, such as “yttrium,” were included in the list to camouflage its real purpose. This was a step we did not want to take, for it automatically pointed out to the press that the government was interested. However, Howard insisted that we simply had to do it if press security was to be maintained. Most reluctantly we agreed. As it turned out, it was a very wise move and an absolutely essential one.

We wished, too, to avoid any widespread mention of such places as Hanford or Oak Ridge and all mention of Los Alamos, as well as any reference to the MED. We also did not want any mention of my name that might arouse the interest of a foreign agent in my activities. Yet to have banned all reference in the near-by papers to Oak Ridge or Hanford would have been neither practical nor desirable, for it would only have tended to attract attention locally. We did try to keep Los Alamos entirely out of the news, but the Knoxville papers were permitted to carry items—mostly in the nature of social notes—about employees and events at Oak Ridge, though nothing, of course, that would help the average reader determine the purpose of the project or its importance. The same leeway was given to the papers close to Hanford.

We did have several unfortunate security breaks, but none of them, so far as we could ever find out, attracted any particular interest. The one with the worst potential for damage was a radio program that discussed the possibilities of an atomic explosion. The script for this had been prepared for the regular news reporter on a network program; he himself had had nothing to do with writing it. Unfortunately, in order to meet his travel schedule, he delivered it from a small affiliated station, where apparently it had not been reviewed to make certain that it did not violate press censorship rules.

From all that we could ever discover, there had been no deliberate breach of security. The information on which the talk was based came from a scientist who was not connected with the project in any way but who evidently had an inkling of what was going on, gleaned, we thought, from some of the project’s scientists at the large laboratory in his city. The actual text was written for the reporter by a friend of the scientist. There was never any question in my mind but that the reporter delivered it in good faith. The failure of the radio station to stop it was attributable to plain carelessness.

Another incident that concerned us greatly was the appearance in a national magazine of an article hinting at the theory of implosion. While it did not violate any rules, it was most disturbing. A thorough investigation indicated that it resulted from the work of an alert and inquisitive reporter in another country.

There was one unfortunate happening not too long before the bombing, when a Congressman, in discussing an appropriations bill, commented on the importance of the Hanford Project. This item was picked out of the Congressional Record and was republished in a newspaper without any comment. I could never disabuse myself of the feeling that this newspaper did it with the deliberate intent of letting me know that our security prohibitions were not so effective as we thought.

Never once, General Groves notes (in Now It Can Be Told: The Story of the Manhattan Project), was any definite country named as the one against which major security effort should be aimed:

At first it seemed logical to direct it toward the Axis Powers, with particular emphasis on Germany. She was our only enemy with the capacity to take advantage of any information she might gain from us.

Japan did not in our opinion have the industrial capacity, the scientific manpower or the essential raw material. Italy was in the same position, with the further disadvantage that any large plants would be exposed to Allied bombing attacks. We did not feel that information secured by Japan would reach Germany accurately or promptly, and we suspected that the Italian-German intelligence channels were not too smooth either.

I had learned within a week or two after my assignment that the only known espionage was that conducted by the Russians against the Berkeley laboratory, using American Communist sympathizers.

[…]

When I was first placed in charge of the MED I found that a number of people in the project had not as yet received proper security clearances, though some of them had been engaged in the work for months.

Any question of the trustworthiness of any one of these people was troublesome, for he would already be in possession of valuable information. To remove him would create only a greater hazard, particularly if he thought our suspicion of him unjustified. (I remembered that Benedict Arnold’s treason had been sparked by his feeling that he had been unfairly treated.) Moreover, if we were to dismiss a person without publicizing the proof, which we would not want to do, the understandable resentment of his friends and associates in the project might seriously interfere with their work.

Almost all our original scientific workers came from academic surroundings. Most of them had been in universities as students or young teachers during the depression years, when there was more than the usual amount of sympathy for Communist and similar doctrines. Almost all of them at one time or another had been exposed to Communist propaganda and had had friends who were secret or even semi-open Communists.

I realized what the temper of the times had been, even though I never had any sympathy for the philosophy or for the educated Americans who adopted it. Discussions with others experienced in this area led me to the belief that among those whose employment would be to the advantage of the United States a reasonable distinction could be made between individuals whose use might be dangerous and individuals whose use would probably not be.

We gave a great deal of weight to how closely the person had followed the party line and for how long. We were particularly interested in how closely he had followed the twists and turns of Soviet relations with Germany. In most doubtful instances this was a deciding factor.

Our problem was made much more difficult by the very limited number of qualified atomic scientists available in this country. We could not afford not to use everyone possible.

The most disastrous break in security was that resulting from the treasonable actions of the English scientist, Klaus Fuchs. Fuchs was born in Germany and had fled to England, where he completed his education. The British authorities had been informed by the Germans prior to the war that he was a Communist. For some reason they ignored this and did not even record the information where they would find it. After the outbreak of the war he was interned as an enemy alien, first in the British Isles and then in a prisoner of war camp in Canada. After some time there he was released and returned to work in England on atomic research. After his return he was made a British citizen.

Our acceptance of Fuchs into the project was a mistake. But I am at a loss when I try to determine just how we could have avoided that mistake without insulting our principal war ally, Great Britain, by insisting on controlling their security measures.

[…]

Since the disclosure of Fuchs’ record, I have never believed that the British made any investigation at all. Certainly, if they had, and had given me the slightest inkling of his background, which they did not, Fuchs would not have been permitted any access to the project. Furthermore, I am sure the responsible British authorities would have withdrawn his name of their own volition, before giving me his history.

If Dr. Chadwick had been in charge of the British mission at that time, as he was later, I am sure that no such deception would have been attempted. Chadwick was always most punctilious in informing me of the slightest question of background, including that of German blood. Unfortunately for the free world, Chadwick did not take over until a few weeks later.

[…]

I have always felt that the basic reason for this was the attitude then prevalent in all British officialdom that for an Englishman treason was impossible, and that when a foreigner was granted citizenship he automatically became fully endowed with the qualities of a native-born Englishman. With the uncloaking in recent years of Fuchs, May, Maclean and Burgess, as well as others, I doubt if this feeling still prevails.

The first uranium separation process General Groves looked into, as he explains in Now It Can Be Told: The Story of the Manhattan Project, involved liquid thermal diffusion:

The basic apparatus is a column. It consists of a long, vertical, externally cooled tube with a hot concentric cylinder inside. What makes this an effective separation method is the fact that one isotope tends to concentrate near the hotter of two surfaces, and then moves upward.

From a practical standpoint, thermal diffusion was not suitable as an independent process because of the incredibly large amount of steam required. The production costs would have been staggering. A minimum rough estimate was two billion dollars, and I would not have considered this a safe figure, but would have raised it to at least three billion if I had thought the work would have to be undertaken.

[…]

However, in June of 1944, Oppenheimer suggested to me that it might be well to consider using the thermal diffusion process as a first step aimed at only a slight enrichment, and employing its product as a feed material for our other plants. As far as I ever knew, he was the first to realize the advantages of such a move, and I at once decided that the idea was well worth investigating.

Just why no one had thought of it at least a year earlier I cannot explain, but not one of us had. Probably it was because at the time the thermal diffusion process was studied by the MED we were thinking of a single process that would produce the final product. No one was considering combining processes.

[…]

To expedite the design and construction, I ordered that, insofar as possible, all process features of our plant, particularly the basic column assemblies, should be Chinese copies of those at the Philadelphia pilot plant. A great deal of time was also saved by frequently using field engineering sketches instead of the customary more formal drawings.

[…]

The basic piece of equipment was the isotope separation column, 102 of which were arranged to form an operating unit which we termed a “rack.” The column was a vertical pipe, forty-eight feet long, of nickel pipe surrounded by a copper pipe. The copper pipe was encased in a water jacket contained in a four-inch galvanized-iron pipe. The copper pipe was cooled with water at a moderate temperature. The columns were arranged in three groups, each of seven racks, making a total of 2,142 columns.

[…]

Sixty-nine days after the start of construction, one-third of the plant was complete, and preliminary operation began.

A Chinese copy, by the way, is an exact imitation or duplicate that includes defects as well as desired qualities. The term goes back to 1844.

The electromagnetic process they implemented at Oak Ridge entailed a number of special hazards, General Groves explains (in Now It Can Be Told: The Story of the Manhattan Project), because uranium is toxic as well as radioactive:

Some of the raw materials were also extremely difficult to handle. High temperatures and pressures were involved and many irritants such as phosgene had to be used. Liquid nitrogen was used in large quantities at a temperature of –196° Centigrade. Huge amounts of electricity were used throughout the process. Each control cubicle, for example, of which there were ninety-six for each alpha track and thirty-six for each beta, consumed about as much electricity as a large radio station.

[…]

We had eight fatal accidents in all of our plant operations through December, 1946. Five people were electrocuted, one was gassed, one was burned and one was killed by a fall.

[…]

Despite all the difficulties that had to be overcome, the first shipment of enriched uranium was sent to Los Alamos in March, 1944, just a few days more than a year after the construction of the plant was begun.

[…]

The chemical side of the electromagnetic process, in fact of the entire project, has often been treated as a simple auxiliary to its more eye-catching atomic physics aspects. Actually, chemistry was the beginning and the end of each of the separation processes. Production efficiency could be won or lost in chemistry, as well as in physics. Each was indispensable.

[…]

The gaseous diffusion process, later termed the K-25 project, was a large scale multistage process for the separation of U-235 from U-238 by means of the principle of molecular effusion. The method was completely novel. It was based on the theory that if uranium gas was pumped against a porous barrier, the lighter molecules of the gas, containing U-235, would pass through more rapidly than the heavier U-238 molecules. The heart of the process was, therefore, the barrier, a porous thin metal sheet or membrane with millions of submicro-scopic openings per square inch. These sheets were formed into tubes which were enclosed in an airtight vessel, the diffuser. As the gas, uranium hexafluoride, was pumped through a long series, or cascade, of these tubes it tended to separate, the enriched gas moving up the cascade while the depleted moved down. However, there is so little difference in mass between the hexafluorides of U-238 and U-235 that it was impossible to gain much separation in a single diffusion step. This was why there had to be several thousand successive stages.

[…]

Without question the most serious problem that confronted us throughout was our inability to produce until late 1944 the barrier material which was the heart of the process. This prevented the orderly installation of the production equipment. It meant that before the first unit could be put in operation, some $200 million had been spent on construction and on the purchase of special equipment, and most of this had been done before we knew even that a satisfactory barrier could be made in the quantities we would require. Yet in spite of this major unknown factor, we had to press ahead with the construction of one of the largest industrial plants ever built, comprising over forty acres of floor space.

[…]

The Oak Ridge plant was a first in every sense, and its design, involving many acres of barrier, was based on this small piece less than two square inches in area. Even this practical foundation soon disappeared when it became known that the material used in the first filter could never be employed in the main plant.

[…]

Finally, after warning us that they were so overloaded with war work that he did not see how they could possibly undertake it, he consented to our talking with his chief engineer. We were amazed when, after we had described in some detail the exacting performance specifications, he replied, “Yes, we can do that. We have already manufactured pumps of the same type, but of course of much smaller capacity.” The contract was accepted and perfectly performed.

[…]

In our hotel rooms we talked at some length about another design problem: how to handle a breakdown within a particular unit. In the course of the discussion, I expressed surprise that it was thought to be a problem, since all that was necessary was to cut out the particular unit that had broken down. The difference between the makeup of the gas varied from diffuser to diffuser so slightly as to be un-noticeable and almost unmeasurable, and I asked how the diffusers could ever tell the difference. That casual question immediately suggested the answer. As so often occurs, it was a case of a simple solution occurring immediately to someone who had not been struggling for months with the problem.

To minimize the effects of gas corrosion, it was first proposed that we use solid nickel for the some hundred miles of process piping. K. T. Keller, the head of the Chrysler Corporation, which was to produce the diffusing units, pointed out that our demands in that case would exceed the entire nickel production of the world, and insisted that heavy nickel plating on the inside of the larger pipe, four inches and above, was feasible. To attempt to heavily nickel-plate the interior of the quantity of pipe we needed was an unprecedented undertaking, but it was solved by a small manufacturer in Belleville, New Jersey, the Bart Laboratories. They developed a novel method in which they used the pipe itself as an electroplating tank. The pipe was rotated during the operation in order to obtain a uniform thickness of deposit. Their success eliminated what otherwise would have been a most difficult situation.

[…]

We had to be absolutely sure that in the hundreds of miles of piping the total leakage of air into the system, particularly through the welds, would not exceed that which would enter through a single pinhole. This problem was solved by industrial engineers. By using helium gas with an improved mass spectrometer, we were able to detect all leaks before the individual piping assembly was installed, and because we could not permit any leakage, no matter how slight, we could not tolerate normal commercial shop welding of the pipe connections, so special welding techniques had to be developed.

[…]

The cleaning and conditioning of equipment prior to installation was vital and the closest practical approach was made to surgical conditions. This involved the complete removal of dirt, grease, oxide, scale, fluxes and other extraneous matter. Any such material, even in small amounts, could very well have caused a complete failure.

The cleaning methods were based on procedures developed by the Chrysler Corporation. The individual steps were not too unusual in industrial practice, but the combination of all of them, their rigorousness and their application to the thousands of pieces of equipment were unheard of.

[…]

All workers changed into clean outer clothing from head to foot upon entering a restricted building.

[…]

Everything possible was done to eliminate dirt and dust. Vacuum cleaners were used instead of brooms, and dust mops were used in order to avoid raising dust by dry sweeping.

Apart from the plutonium plant at Hanford, General Groves explains (in Now It Can Be Told: The Story of the Manhattan Project), the heart of the effort to produce material for a fission bomb was Oak Ridge:

Here were located all our uranium separation plants — the plants designed to separate the easily fissionable Uranium-235 from the more abundant but much less fissionable isotope, Uranium-238. There were a number of ways we thought this could be done, but for practical reasons, to suit our immediate purposes, they were whittled down to two, the electromagnetic process and the gaseous diffusion process.

[…]

We had decided at the start that the several uranium process plants at Oak Ridge should be well separated, so that in case a disaster struck one it would not spread to or contaminate the others. For that reason, the electromagnetic and gaseous diffusion plants were located in valleys some seventeen miles apart. Later, when the thermal diffusion plant was built, we had to disregard this policy and put it quite near the steam-generating plant for the gaseous diffusion process, in order to take advantage of its supply of extra steam.

[…]

It is a physical rather than a chemical process, although a great deal of chemistry is involved in the handling of the material. Basically, electromagnetic separation of isotopes is based on the principle that an ion describes a curved path as it passes through a magnetic field. If the magnetic field is of constant strength, the heavier ions will describe curves of longer radii. Therefore, the various isotopes of an element, since they differ in mass, can be isolated and collected by such an arrangement.

[…]

Rather early in the American effort, Lawrence had proved to his own satisfaction that electromagnetic separation was feasible, but he stood almost alone in this optimism. The method called for a large number of extremely complicated, and as yet undesigned and undeveloped, devices involving high vacuums, high voltages and intense magnetic fields.

[…]

Dr. George T. Felbeck, who was in charge of the gaseous diffusion process for Union Carbide, once said it was like trying to find needles in a haystack while wearing boxing gloves.

[…]

The first estimate for construction alone was for an unrealistic sum of between $ 12 and $ 17 million; soon afterward this was increased to $35 million. These figures were for a plant much smaller than the one we finally built. In its first report to President Roosevelt early in December, 1942, the Military Policy Committee estimated the cost of the entire project as of the order of $ 400 million. At that time we thought that over $100 million would be needed for this process as a whole.

[…]

Exclusive of the value of silver borrowed from the Treasury for electrical conductors, the construction costs, by December 31, 1946, totaled $304 million; research cost $20 million, the engineering $6 million and operation $204 million. The cost of operating power was almost $10 million.

[…]

Originally we had thought we would need a work force of 2,500. This was a sad underestimate, resulting from our inability to anticipate how complex and difficult the job would be and how many units would be needed. Eventually we had over 24,000 on the payroll.

[…]

We could not permit or even consider the unionization of the operating forces of any of the plants turning out U-235 because we simply could not allow anyone over whom we did not have complete control to gain the over-all, detailed knowledge that a union representative would necessarily gain.

[…]

Later, when our needs grew even more pressing, we were unable to find enough pipe fitters to maintain our schedule. Investigation showed that there simply were not enough in the United States to fill the demands. The solution we adopted was to locate a considerable number of pipe fitters, all union members, who had been inducted into the Army. These men were given the opportunity to be furloughed to the inactive reserve on condition that they would accept employment at Hanford as civilians at the going rates of pay.

When they arrived they were kept together as a group so that their output would not be held down by the pressure of any union officials or of the men already working there. In a direct comparison on identical work, they produced about 20 per cent more than the other men. Pressure was brought on them to slow down, but they refused. A typical comment was: “I’m not working as hard as I did in the Army, nobody’s shooting at me, I’m being paid a lot more and, what’s more important, I’ve a lot of friends in my old outfit that I hope to see come back alive.” As time went on, the other men were apparently shamed into greater effort, with the result that their output went up about 10 per cent.

[…]

On my next visit to Oak Ridge I talked for five or ten minutes to some two thousand of these men. I was not introduced by name but merely as the general in charge of the work for the War Department. The reason for this was to avoid drawing attention to me personally; this was our policy throughout the project until security no longer required it. (My wife once commented that I was undoubtedly the most anonymous major general in the history of the United States Army.)

As simply as possible, I told the group that, as the officer in charge, I could state positively, both officially and personally, that their work was of extreme importance to the war effort, and that my views were a true reflection of those of the Chief of Staff, General Marshall, of Secretary of War Stimson and of President Roosevelt. I added that they could see for themselves how important it was from the terrific effort we were making, our obviously enormous expenditures in money and labor, and our evident ability to obtain materials that were in critically short supply. I said nothing about what we were working on or our hope that its success would quite possibly end the war. There was no flowery oratory; I would have been incapable of it, and it certainly would not have appealed to the audience.

Creedon estimated that after this meeting the efficiency of his construction operations improved by as much as 15 to 20 per cent. I never quite believed this, but the progress reports did indicate an increase of well over 10 per cent. This was far beyond anything I had anticipated; indeed, I would have been pleased with any improvement at all.

[…]

Although we were certain sabotage was not involved [in the “snag” with the magnets on the “race track”], in our detailed review of the situation we found that it would be possible for a saboteur, who would have to be an employee on one particular assignment, to throw iron filings into a feed opening in the oil circulation system and thus put an entire section of track out of action. Steps were taken at once to station counterintelligence agents on and around these spots.

One difficulty, which was unforeseen, because we lacked experience with magnets of such enormous power, was that the magnetic forces moved the intervening tanks, which weighed some fourteen tons each, out of position by as much as three inches. This put a great strain on all the piping connected to them. The problem was solved by securely welding the tanks into place, using heavy steel tie straps. Once that was done, the tanks stayed where they belonged.

[…]

Other substances that had previously had very limited application were needed in staggering quantities. For example, each alpha track used four thousand gallons of liquid nitrogen every week.

One incident that delayed production on a bin in an alpha track for several days involved a mouse. In some unknown way, he got into the vacuum system, where his presence prevented the bin from reaching the necessary high vacuum. After several days of trouble-shooting failed to reveal the source of the trouble, the run was terminated and the bin opened. The remains of the mouse, a bit of fur and a tail, disclosed what had caused the trouble, but no one ever learned how he got into the system in the first place.

More serious in effect was the suicidal action of a bird which perched on an outside wire in such a way as to short the electrical system. We had to shut down an entire building, and, because of the nature of the process, it was several days before operations again became normal.

[…]

Waste such as piping, scrap cloth, filter cloths, papers, rubber gloves, clothing and the like had to be carefully saved in order to recover the small concentrations of uranium, particularly of Uranium-235.

I don’t know if you caught that passage about the costs: “Exclusive of the value of silver borrowed from the Treasury for electrical conductors, the construction costs, by December 31, 1946, totaled $304 million; research cost $20 million, the engineering $6 million and operation $204 million. The cost of operating power was almost $10 million.”

Exclusive of the value of silver borrowed from the Treasury for electrical conductors?

Preliminary design calculations on the Y-12 electromagnetic plant in the summer of 1942 had indicated that enormous quantities of conductor material would be required. Because the demands for copper to be used in defense projects far exceeded the national supply, the Administration had decided that the need for copper should be reduced by substituting for it silver borrowed from the Treasury Department.

Colonel Marshall thereupon called on the Under Secretary of the Treasury, Daniel Bell. Mr. Bell said that he might be able to make available some 47,000 tons of free silver, together with 39,000 tons more which could be released from the backup of silver certificates, if Congress authorized its use through appropriate legislation. At one point early in the negotiations, Nichols, acting for Marshall, said that they would need between five and ten thousand tons of silver. This led to the icy reply: “Colonel, in the Treasury we do not speak of tons of silver; our unit is the Troy ounce.”

Under the terms of the final agreement, the silver required by the project was to be withdrawn from the West Point Depository. Six months after the end of the war an equal amount of silver would be returned to the Treasury. It was further agreed that no information would be given to the press on the removal of the silver, and that the Treasury would continue to carry it on their daily balance sheets. Our relations with the Treasury were most cordial, and Mr. Bell and the various officials of the Mint and the Assay Office were always very pleasant and helpful.

Because of the natural reluctance of any private company to accept the responsibilities for safeguarding and accounting for the large amounts of silver that were involved, the MED had to carry out this responsibility with its own forces. This meant organizing separate guard and accountability units, establishing special inspection procedures employing special consultants and arranging to convert the silver into the conductors that we so urgently needed.

We accepted the Treasury’s certification of the bar weights of the silver as we took it over at West Point. Then we delivered it to a processor, who cast the bullion bars into billets which could be extruded into forms more suitable for manufacture into bus bars, magnet coils and similar items. The casting was done by the Defense Plant Corporation and by the U.S. Metal Refinery Company. For the large magnets which used the bulk of the silver, Phelps Dodge Copper Products Company then extruded the billets into strips, which were rolled into coils about the size of a large automobile tire. These coils were shipped to Allis-Chalmers, where they were wound, suitably insulated, around the steel bobbin plate of the magnet casing.

Special MED guards watched the silver at all times while it was being processed, and accompanied every shipment except that of the final magnets from Allis-Chalmers to the Clinton works. We decided that at this point we could achieve adequate security by sending unguarded railway cars over different routes on varying time schedules. The silver coils were encased in large, heavy, steel shells which were completely welded together. Although silver is a valuable commodity, to have made away with any great amount of it during shipment would have been a major task, as our experience in opening one of these shells at Oak Ridge later confirmed. Moreover, the railroads always followed our shipments carefully, and we would have known immediately if any car had been waylaid.

[…]

No recovery operation was undertaken unless the recoverable amounts were expected to be of more value than the cost of recovery. Nevertheless, throughout the entire operation we lost only .035 of one per cent of the more than $300 million worth of silver we had withdrawn from the Treasury.

That’s still $105,000, by the way — and back when that meant something.