ROSS GUNN AND THE NAVAL RESEARCH LABORATORY’S EARLY RESEARCH INTO NUCLEAR PROPULSION, 1939-1946

Mr. Ahern is Senior Archivist of University Archives, University of Pennsylvania. When he wrote this he was Assistant Manager of Technical Services with American Philosophical Society. This article first appeared in the Spring, 2003 issue of the Journal Historical Studies of the Physical and Biological Sciences. It is reproduced here with permission from the University of California Press.

The following abbreviations are used: APS, American Philosophical Society; Bowen Papers, Mudd, Harold G. Bowen
Papers, Public Policy/University Archives, Department Rare Books and Special Collections, Princeton University Libraries; BP LOC, Papers of Harold Gardiner Bowen, Manuscript Division, Library of Congress, Washington, D.C.; NACP, National Archives and Records Administration at College Park, College Park, MD; NAMA, National Archives and Records Administration-Mid-Atlantic Region, Philadelphia, PA; NBL AIP, Niels Bohr Library, American Institute of Physics, College Park, MD; OA NHC, Operational Archives, Naval Historical Center, Washington, D.C.; SCOA, U.S. Senate Special Committee on Atomic Energy, Atomic energy: Hearings pursuant to S. Res. 179.79^th Congress, 1^th sess, 13, 14, 19, and 20 Dec 1945.

On September 30, 1954 the United States Navy commissioned USS NAUTILUS (SSN-571 ), the world’s first nuclear powered vessel. Credit for making NAUTILUS a reality goes to Admiral Hyman G. Rickover, who, as a captain, was assigned to the Bureau of Ships in 1947 to look into the potential of nuclear propulsion. He later became head of the Division of Reactor Development at the U.S. Atomic Energy Commission and Director of the Naval Reactors Branch in the Bureau of Ships. While Rickover’s engineering and managerial skills provided the impetus for the creation of NAUTILUS, the concept of a nuclear powered submarine dates back to 1939 and Ross Gunn, a research physicist and technical advisor at the Naval Research Laboratory (NRL). Between 1939 and 1946 Gunn directed research at NRL to determine the feasibility of using nuclear energy for submarine propulsion. Though historians mention NRL’s work during this period, its influence is regularly overlooked. Naval historian Gary Weir: “historians interested in the naval nuclear propulsion program, and determined to establish cause and effect firmly and clearly, have failed to evaluate properly the elusive influence of the compelling ideas emerging from NRL in the early postwar years.”

Why has the influence of NRL been overlooked? Anny, that is, the Manhattan Engineering District (MED) controlled all matters relating to the atom bomb project. ln their efforts to solve the key problems of nuclear propulsion, Navy scientists developed methods for the production of uranium hexafluoride and for isotope separation using liquid thermal diffusion. Both of these methods, vital to the production of uranium 235, were used to create the atomic bomb. However, the Navy’s research was carried out in isolation from and in competition with MED.

With the support of NRL directors Admiral Harold G. Bowen and Admiral Alexander H. Van Keuren, Gunn struggled with MED to get the supplies the program needed and to show the potential of the research to the overall program. Philip Abelson (physicist at Carnegie Institute) later commented, ” [i]n my dealings with Ross Gunn, I noted that in a situation where he was certain of the facts, he did not avoid conflict, and he was resourceful when in a fight.”1 The correspondence and files of Gunn and his associates document their confidence in their work illustrate the early influence of the NRL program on the development of nuclear energy, and reveal the affect of the postwar focus on MED and Rickover on Gunn. The Navy, not the Anny, deserved credit for laying the groundwork for nuclear energy in the United States. Although the atomic bomb was built by the Manhattan Engineering District under General Leslie Groves, the little-known and nearly suppressed story of the Navy’s prior work in this field gives credence to Gunn’s claim that the Navy got hosed.

1. NAVY’S INTEREST AND RESEARCH

Early interest

The U.S. Navy’s interest in developing a nuclear powered submarine originated in the separate quests to find an ideal means of submarine propulsion and a new power source for naval vessels in general. Discussions over the role and mission of the submarine in the Navy date back to 1911 when the General Board determined that submarines would have two roles- coastal protection and fleet operations. For fleet submarines the important task became finding the best means of propulsion to meet their mission requirements. In 1912 the Navy adopted diesel-electric engines, which required that the submarine carry both fuel and oxygen to operate when submerged, restricting its range and speed. Even before the end of World War I the search began for a new means of propulsion. Inside the Navy, Gunn was alarmed at the nation’s disappearing coal and oil reserves. To him, the Navy had an obvious interest in new forms of power given its position as one of the world’s largest consumers of petroleum.

NRL’s Mechanics and Electricity Division was responsible for investigating new power sources and their application. During the early 1930s the division, headed by Gunn, studied new power plants for submarine and torpedo propulsion. Among those under consideration were the fuel cell, the hydrogen peroxide-alcohol steam turbine, and diesel engines operated in a closed cycle. The central limitation in all of these methods was the need for adequate oxygen for propulsion under water and a means of regeneration when running on the surface. The possibility of nuclear energy was very intriguing. According to Gunn, “[i]t was recognized immediately [after the discovery of fission] that perhaps here was an answer to the submarine propulsion problem.” Nuclear power would simultaneously remove the oxygen problem and provide the submarine with a long cruising range. Gunn ‘s division had numerous discussions about the application of the nuclear energy to naval problems but decided not to present a research program to the nononsense Navy bureau chiefs until they had significant data to back it up.

While scientists at NRL theorized about the use of nuclear energy, it was Enrico Fermi’s meeting with Navy representatives in March 1939 that gave nuclear energy research its start at the laboratory. On March 16, George Pegram, dean of the Graduate Physics Department at Columbia University, wrote Admiral Stanford C. Hooper, director of the Technical Division in the Office of the Chief of Naval Operations, about the possibility of using uranium to create a nuclear weapon. Although Pegram doubted that the project would succeed, he, Fermi, and Leo Szilard thought that the potential should not be ignored. “[T]here is no man more competent in this field of nuclear physics.” Pegram wrote two months after Niels Bohr had discussed the discovery of fission with Fermi; his letter to Hooper was the first attempt by scientists to get the United States government involved in nuclear research.

Beginning of NRL nuclear research

The meeting with Fermi on March 17 at the Navy Department building on Constitution Avenue was attended by representatives from the Navy’s Bureaus of Engineering. Ordnance, and Construction and Repair, NRL, and the Army’s Ordnance Department. In a little over an hour Fermi discussed the discovery of fission, the potential of an atomic bomb, and the possibility of a nuclear power source. Fermi left the meeting feeling that it had yielded little, even though a Navy spokesman said the service was anxious to keep in contact with his work at Columbia University and would have representatives call in person. Fermi had not realized that he had given the NRL representative, Gunn, the evidence that he needed to take his division’s idea before the Bureau of Engineering. Three days after the meeting Gunn and Captain Hollis M. Colley, director of the NRL, approached Admiral Harold G. Bowen, director of the Bureau of Engineering, with a request for $1,500 to start uranium research. They outlined the probable operational and military capabilities of a nuclear submarine. When Gunn and Cooley left Bowen they had their funding and within a week had begun research, to “the first organized program in nuclear research in this country at the Naval Research Laboratory.” NRL’s work began almost seven months before President Franklin D. Roosevelt received Albert Einstein’s famous letter about the potential for an atomic bomb.

The first official memorandum on the basic problems of nuclear powered submarine propulsion was prepared on June 1, 1939. In it Gunn stated that a uranium power source could provide heat to run a steam power plant without requiring “the oxidation of organic material” or that “oxygen be carried down in the submarine.” It remained to design a method to obtain the uranium 235 that Bohr had identified as an ideal source for a chain reaction. “[1]f the method will work, it is of outstanding importance and will greatly modify the experimental program at this Laboratory. If it will not work, it is of utmost importance to determine this fact at the earliest practicable date.” The Navy did not have a weapon as its primary objective. Gunn again: NRL “realized the two important solutions would fall out together… and we knew that if we could solve the power problem the bomb application would automatically come out with a very small amount of additional work.” Further, Gunn believed, or hoped, that the United States would not have a cause to use such a horrible weapon.

Before separation research could begin, NRL needed an adequate supply of uranium hexafluoride (UF6 or hex), which exists in either a gaseous or liquid state under ordinary conditions. R. R. Miller of NRL’s Chemistry Division and T.D. O’Brien of the University of Maryland began working in April 1939 on hex production. The method they developed passed fluorine gas over a powdered uranium-nickel alloy that “was expensive and laborious to make.” the initial samples produced lacked the purity needed for use in isotope separation. By January 1940, after nine months of work, NRL could produce pure gram-sized samples of uranium hexafluoride.” While the Miller and O’Brien method allowed NRL enough pure hex for research, it could not meet all research and production requirements. The difficulty of making the uranium nickel alloy kept hex production to “a hundred grams.

Physicist Philip Abelson at the Carnegie Institution of Washington required more than ten times this amount for his experiments. Abelson set out independently to make UF6 without using the alloy. With the help of H.B. Knowles, Abelson devised a straightforward method using a common salt of uranium that yielded nearly a kilogram of hex per day by July 1941.9 With the success of Abelson’s method, NRL began to arrange for the commercial production of UF6 in October 1941. Following the approval of the Uranium Committee, which oversaw uranium research in the United States, the Navy asked the Harshaw Chemical Company of Cleveland for an estimate for producing hex in 50-pound lots. Harshaw Chemical had received authorization to begin UF6 production by December 1941.

Once NRL had overcome the hex of hex, it turned to isotope separation. NRL contracted research out to laboratories at some of the nation’s top universities and research institutions. Four methods (gaseous diffusion, ultra centrifuge, mass spectrograph, and liquid thermal diffusion) were developed far enough for trial in pilot plants.
Columbia University received $30,000 to study centrifugal fractionating columns; the University of Virginia, $13,000 to carry out the early phase of research on high-speed contrifuges. The Carnegie Institution of Washington conducted research on liquid thermal diffusion under Abelson, at first as a public service and later with an allotment of $3,500. Gunn judged it “a forward-looking program that would ultimately lead to a power-producing pile.” The program was financed by the Army’s Ordnance Department and the Navy’s Bureau of Ships and Ordnance, with NRL coordinating the work.

The Carnegie Institution received the Navy’s first contract. Lyman J. Briggs, director of the National Bureau of Standards and chair of the Uranium Committee, recommended to Bowen that NRL enter into a contract with John A. Flemming at the Carnegie Institution to support Abelson’s research. Abelson had joined the Institution’s Department of Terrestrial Magnetism in August 1939 from the University of California at Berkeley to design a 60-inch cyclotron. Abelson became interested in liquid thermal diffusion in July 1940, when Gunn visited him with a copy of Progress Reports in Physics that contained an article by H.C. Urey reviewing all of the known methods for isotope separation. “Gunn suggested that I look into the methods to see if I could find any that looked promising …. [A] review of the literature showed that…thermal diffusion had considerable promise, especially because it appeared that considerable quantities of material might be handled by this method.” The basis of the method is that lighter isotopes diffuse more quickly than heavier ones against gravity toward the warm side of a temperature gradient: material rich in uranium 235 would move to the top of a column sustaining a gradient.

Initially liquid thermal diffusion had not been considered a practical method for isotope separation. Research at four laboratories in the United States had shown that gaseous thermal diffusion did not give measurable separation. Abelson’s first columns at the Department of Terrestrial Magentism proved successful. He formally suggested using liquid thermal diffusion in a l 7-page memorandum in September 1940. During this preliminary period he had his salary from the Carnegie Institution, his equipment from NRL, and laboratory space and a chemist from the Bureau of Standards. On June l, 1941 Abelson became a Navy employee and transferred his work to NRL ‘s Anacostia Station. The preliminary work with eleven liquid thermal diffusion columns 1.5 inches in diameter and from l to 12 feet long showed that temperature differences and wall spacing were the critical variables. Abelson points to the simplicity and low startup cost of the process as demonstrated by the speedy construction of the first plant. The main disadvantage was the large requirement for steam. Gunn thought Abelson’s separation process promising and kept a close eye on it.

Around June 1, 1941, the NRL began to construct a small pilot plant with 36-foot columns next to its Boiler House. “[1]t was felt that a number of columns should be built possessing various spacings and that these columns should be tested at temperatures as high or even higher than the critical temperature of UF6.” NRL installed a high-pressure, gas-fired boiler that could deliver 750 pounds of steam per hour at a pressure of 600 lbs./in2. Construction ended November 1, 1941, delayed by parts suppliers. Over the next six months NRL staff experimented with the spacing for the interior of the columns and their continuous operation. They found that the optimum spacing declined slightly as the temperature difference went up. The columns showed no considerable corrosion. Encouraged by these findings NRL decided to build fourteen 48-foot columns; authorized in July 1942, the installation was substantially completed by November. 13 Since the Navy was focused on submarine propulsion they chose to use an enrichment method that would provide quantity over quality. In supporting the decision to pursue liquid thermal diffusion, Bowen pointed to its many advantages for production under war conditions.” It was not optimal because of its high consumption of power. For NRL the next step was designing a full scale plant.

Army-Navy rivalry

By December 1942 the Laboratory had ten to fifteen columns up, running and producing accurate, usable data. On December 10 General Leslie R. Groves and other representatives of the Army’s Manhattan Engineering District visited the NRL plant. Gunn: “a rather complete review was given of the Naval Research Laboratory’s research interest in this project in its earliest days, and our part in the preparation of uranium hexafluoride for the original work was emphasized.” NRL provided all the information it had. The Anny desired detailed information on the pilot plant’s performance. NRL could not supply it since the plant had been operating for only a month. NRL then learned that MED had been placed in charge of isotope production by order of the President, and that since the project was regarded primarily as a matter of construction, a civil engineer had been placed in charge. Gunn was not happy with the situation. “[N]one of these gentlemen [in Groves’ group] are … familiar” with isotope separation, and would regularly require “expert advice from those actually engaged.” What most irritated Gunn was the Navy’s lack of representation, “the Navy is not represented on any committee except indirectly through Admiral [W.R.] Purnell, who has no direct access to technical information on the matter.” An advisory committee from MED followed up Groves’ visit in early 1943 and took a favorable view of NRL ‘s work. However, the use of liquid thermal diffusion by MED was “vetoed by higher-ups and nothing was done.” Groves decided that liquid thermal diffusion required too much steam. Groves rated NRL’s research as “most competent” but “extremely limited,” and the size and pace of the Navy project did not impress him. Finally transfer of the Navy program to MED would have major administrative and security problems.

What finally kept the Navy outside the nuclear research program was an order by President Roosevelt. When Vannevar Bush, director of the Office of Scientific Research and Development (OSRD), heard that Groves intended to visit NRL, he considered it a mistake. Bush had recommended the creation of the OSRD (authorized in June 1941), to advise the president on scientific matters and coordinate research at the various governmental laboratories. Bush had advised Roosevelt to exclude the Navy from nuclear research, perhaps because Bush had influence over and confidence in the War Department, especially Secretary of War Henry Stimson. Bush’s dealings with the Navy had been bumpy. Bowen had criticized OSRD for supplanting the service laboratories and taking needed funding from NRL. Bush had no qualms about reciprocating. Only a few naval officers and civilian engineers joined the MED. When the Uranium Committee became the S-1 Committee of OSRD, all Navy members were dropped. “[T]he Uranium Committee which previously had guided atomic research policy was quietly put into the background and the proper degree of exchange of information between laboratories was stopped.” This further isolated the Navy’s work. Finally, Abelson’s findings were not available until after Roosevelt set up the MED in September I 942. The Army developed a $2.5 billion project while the Navy conducted preliminary research on what was considered a secondary separation process.

Still NRL was allowed to continue its research on separation to determine if thermal diffusion could be useful to the MED. A report of September 1943 stated that the NRL process was “extraordinarily attractive because of simplicity of equipment and operation” despite its drawbacks of slowness and steam consumption; and recommended that the NRL program should be included in MED “in its present state … because of its ultimate potentialities.” Meeting a week later, the S-1 Committee decided that “it would be most unfortunate for the entire efforts if any further expansion of the work at the Naval Research Laboratory in this field were to result in the drawing away of personnel now being employed on other aspects of this program” NRL could continue, but on a small-scale.

Naturally, Gunn was not happy at being excluded from the main research program. By 1943 MED hadexpendedover$2,000,000, the Navy only $60,000. Gunn, “According to Dr. [E.V.] Murphree … the Naval Research Laboratory method is the furthest along in development and the best engineered of any competing separation process.” It had been treated unfairly: “The production requirements set by the S-1 Committee gave their method an unusual advantage over ours.” Since NRL had been involved from the beginning, Gunn felt that it was not “in the best interest of progress” to exclude the Navy from further work. As he saw it, NRL was “a military laboratory entitled to have access to any information in the country available on this subject.” Admiral Alexander H. Van Keuren, who became director of NRL in 1942, was equally outraged by the Army’s expenditure of “astronomical sums” while the Navy had “independently carried forward a fruitful research program” at considerably less cost. “The history of liquid thermal diffusion at this laboratory has been one of continuing improvements in results.

Philadelphia plant

In January 1943 Abelson noted that “the apparatus [seemed] to be unusually dependable and capable of long time trouble free operation.” Isotopes could be separated by the thermal diffusion method of isotope separation on a large scale. However, additional research had to precede a production plant. Abelson made estimates of a 100-unit plant, which could be operational by July 1, 1944. The primary objective of the suppositions plant was “to obtain a real engineering basis for the erection of a large scale installation.” Between February and July 1943 NRL constructed eighteen columns, which it operated for 1,000 days. During this period NRL realized that its steam facilities could not support larger columns. They sought a new steam source. The first site examined was the
Naval Experiment Station in Annapolis, MD. To obtain the necessary amount of enriched uranium for a chain reaction a 300-column plant would have to run for 270 days. To install such a facility in Annapolis would cost $2,500,000. Finding this option too expensive, NRL made a review of other naval facilities and came across the Naval Boiler and Turbine Laboratory (NBTL) at the Philadelphia Navy Yard.

NRL proposed the construction of a “larger pilot plant or a small production plant” at the Philadelphia Navy Yard in June 1943 to “separate uranium isotopes by our method, with the object of providing insurance against the complete failure of the Manhattan Project.” On July 24, 1943 Van Keuren, Gunn, and Abelson visited NBTL to determine if steam production and available facilities would meet their research needs. NBTL estimated that it would cost $500,000 and a support staff of 40 to modify its equipment to provide the steam required. Eleven days later representatives of NRL and NBTL agreed that NRL’s research would move to the Philadelphia facility. The site had building space, cooling water, and engineers with considerable experience in “high-pressure steam and large scale heavy construction.” Abelson stressed that the plant should run continuously, “and asked whether the two pumps on the forced circulation boiler could be arranged so that the second would be cut automatically, in case of failure of the other.

NBTL representatives informed NRL that if they wished to have the plant completed and operational by the beginning of 1944 they would need to bring in an outside contractor because of the work load at the Philadelphia Navy Yard. While NRL was aware that the project would put strain on the Philadelphia Laboratory, they were confident that it could be undertaken with “[c]arefully coordinated teamwork.” Gunn requested that both the Public Works Office at the Philadelphia Navy Yard and NBTL be instructed that the project had “priority.” These requests probably resulted from the NRL’s growing difficulty in getting assistance from the Anny. Admiral Earle Mills, assistant chief of the Bureau of Ships, signed the order on November 17, 1943 that authorized NRL to construct a 300-column pilot plant in Philadelphia, with the stipulation that they not use technical personnel possibly needed by MED.

The NBTL informed the Bureau of Ships on December 1, 1943 that NRL ‘s research work was assigned to the boiler division, given project number 2715, and the title “Reflux condensers, Naval Research Laboratory.” The building NBTL made available had been designed to test turbines. Using half of the building, the site housed three racks as well as the necessary steam-generating equipment. The space just allowed for a distance of 56 ft between the pit floor and the roof truss, the minimum needed for the columns. On December 22, Van Keuren contacted Admiral Allan J. Chantry, commandant of the Philadelphia Navy Yard, to request that he assist NBTL as frequently as possible. “[W]ithout knowing too much of the progress which our enemies are making along similar lines, we feel here at the Laboratory that they may be ahead of us, and therefore in a position to spring unpleasant surprises on allied countries before we are ready to retaliate.” Construction on the Philadelphia plant began on January 1, 1944: “[T]he cooperation of the Administration Officers and employees of the Naval Boiler and Turbine Laboratory has been
excellent and they are doing everything they can to expedite this project in the face of a serious skilled labor shortage.”22 In May 1944, Abelson wrote that progress in Philadelphia was “moving along satisfactorily,” even though finding the necessary manpower was difficult. He expressed that the 100-column machine would be completed by July 15. Although the plant could then be increased to 300 columns, NRL was “not particularly anxious to take on a routine production job.” They did not want to stop experiments on improving performance.

Hindered access

MED hindered NRL’s access to information and materials. By the beginning of 1942 NRL no longer received information from the S-1 Committee. The Navy could not proceed further without information from the Army. Gunn would not spend money on duplicate research. Abelson also complained about the lack of exchange of technical information. Van Keueren joined in: ” [t]he scientific mind works best when it has all the information available on a subject, and the whole problem is of such extreme importance to the Navy that every means should, in my opinion, be adopted to forward it.” NRL and MED had no contact between September 1942 and April 1943.

MED blocked or hindered NRL’s acquisition of material. In January 1943 NRL was informed that it would have to go through the Army to obtain supplies of UF6. The S-1 Committee decided that around Labor Day 1943 NRL would not receive new supplies of uranium hexafluoride, even though it asked NRL to exchange enriched material for normal UF6. When NRL requested supplies of UF6 in October, Groves refused, “for an indefinite period.” NRL protested that Abelson had developed the method of producing uranium hexafluoride, and that it had freely shared the information. The Army reluctantly supplied the material. Then, all information exchange between the two projects stopped again. In November MED ordered the War Production Board to withhold UF6 supplies from NRL. Gunn: “it took months of strenuous effort, in the midst of war, to get this sordid and incredible political action reversed.

The Army controlled the nation’s entire raw uranium supply and hence the commercial production of uranium hexafluoride. Abelson learned from Richard Lund at the Rare Minerals Division of the War Productions Board that the monopolists had told him not to give NRL additional uranium. Gunn naturally regarded the order as “unwarranted, unjustified and manifestly an attempt to override the best interests of the Navy in this work.” He did not see how his request for a mere 2,000 pounds could effect or jeopardize the Army’s project. He mobilized his superiors. Van Keuren contacted Groves at the request of Mills. He reminded Groves that the S-1 Committee had decided that NRL should continue its research “on a small scale… as an insurance against the failure of the isotope separation project…[T]his material is essential for the completion of the present phase of the Navy’s work on isotope separation.

After excluding the Navy from the main program, the Army decided to use the electromagnetic and gaseous diffusion processes for isotope separation. As the Philadelphia plant neared completion in Spring 1944, MED had only its electromagnetic plant in operation and so began looking at other separation methods it had discarded earlier. J. Robert Oppenheimer took an interest in liquid thermal diffusion after reviewing two year-old reports on Abelson’s works and updates from Captain William S. Parsons, who had made inquiries about the Philadelphia plant and calculated that the steam power available at the Philadelphia Navy Yard could run one three times as large. Oppenheimer considered using enriched uranium as a feed for the other processing plants to speed up production: Groves did not favor the Army’s using the Navy’s process. A review committee composed of MED scientists and others went to Philadelphia in mid-June 1944 and recommended the construction of a liquid thermal diffusion plant at Oak Ridge. On June 26 Groves and some advisors including the physicist Richard Tolman went to NRL to obtain the blueprints for the Philadelphia plant. The Army broke ground on July 6 for its plant, labeled S-50 and had the first columns ready by September 15.

Philadelphia accident

The Army lacked trained personnel to build and operate the S-50. Groves sent four civilians and ten Army enlisted men to the Philadelphia Navy Yard for training in August 1944. The Army personnel were drafted engineering graduates given the rank of private first class A week after arriving in Philadelphia on September 2, they were involved in the plant’s only accident. At 1 :20 p.m. a cylinder of UF6 in the transfer room exploded, fracturing nearby steam pipes. Samuel B. Weir, superintendent of power transmission at NBTL, witnessed the accident, which occurred as Weir’s team tried to improve the valves between the uranium hexafluoride and the pilot plant. A bottle containing 600 pounds of UF6 overheated and exploded. “The bottom blew off the bottle, and the gases escaped like a jet, sending the bottle crashing through the wall of the building.” The mixture of UF6 and steam created hydrogen fluoride, a very caustic acid.

It caused violent sickness. The men made for showers that had been set up outside. The injured were taken to the Philadelphia Naval Hospital; thirteen men hd been hurt and two of them died. Although NRL worried about security leaks, the incident went unnoticed, blending into the regular industrial accidents that occurred at the Navy Yard during the war. What set the explosion apart was that the casualties included Army enlisted personnel. The headline in the Philadelphia Evening Bulletin read, “2 Killed, 9 Hurt by Blast that Blows Out Side of Navy Yard Building.” The article gave a list of the dead and wounded, and noted that five soldiers were among the casualties. The article gave no cause for the accident. The entry in the Yard’s log book read, “[t]he weld of a steel high pressure gas flask carried away a small building south of Building No. 683. The force of the escaping gas injured a number of men working in the vicinity, some seriously, and damaged the side of the frame building in which stored.” The Beacon, the Philadelphia Navy Yard’s newspaper did not mention the incident.

The accident halted the training of army personnel in Philadelphia. All of the Army trainees and fifteen men from NRL under Abelson went to Oak Ridge, “where preliminary conditioning of equipment began on I 0 September.” Then a thorough investigation into the accident assigned its cause to the design of the tanks and the lack of cooperation from MED. In a meeting between NRL and the Anny, ” [i]t was pointed out that the Navy had attempted to secure seamless nickel tubes, but because the Anny had preempted all facilities for the production of nickel materials we could not get them.” To compensate, NRL had built the new tanks of “a thin nickel inner-liner carefully gas-welded and free of leaks, which fits very closely in a very strong alloy steel container.” Gunn asked how the Army had reached it conclusions. An Army representative replied that “he had been specifically ordered not to disclose the basis of his calculations.” This did not sit well with Gunn. He concluded this memo on the meeting: “[B]ecause we cannot check nor understand the details of the estimates we are forced to assume that the Army group’s calculations are infallible, an assumption which I am not ready to make. To my mind this leaves the Laboratory in a very bad position and our only defense in an event of a real serious accident would be the statement that the Army had given the Navy certain assurances. In view of the circumstances I consider it essential that the Naval High Command make further representation to the Army authorities for this project.

Repairs were quickly made to the Philadelphia plant. Its work was critical to the development of the atomic bomb. Besides providing a guide for the construction of the larger plant at Oak Ridge, it produced enriched uranium. Over 5,000 pounds were turned over to MED to feed the electromagnetic isotope separator, which contributed to the construction of the first nuclear bombs. According to Gunn, “the national production of uranium for the atomic bomb was increased by 20% through the erection of the Oak Ridge Plant.” Thus NRL ‘s expenditure of$2,000,000 was critical to the timely production of the atomic bomb. “[W]e were credited with shortening the war by a week or more, in spite of the delaying tactics and fumbling politics imposed on us by some members of the Manhattan Project.” In testimony before the Senate, Gunn said, “we think that by means of our very early work we have shortened the time it took to produce the critically required material. If we had not worked on the thing at the start and early supported these university people we think perhaps the national production might have been delayed.

The Philadelphia plant continued to operate after the S-50 plant was shut down. A memo from NRL to NBTL specified that upon completion of the current work, “the project be temporarily closed and no further work carried out.” The personnel there were to maintain the plant to allow it to resume operation within thirty days of notice. However, it was not to be dismantled “until a more definite policy on a high level is promulgated.” NRL personnel went back to Washington, and their former work place began a training ground in the proper use of radiation detection instruments in preparation for Operation Crossroads. In September 1946 it was decided to dispose of the Philadelphia plant. Following a telephone conference with Groves, Mills informed the Commander of the Philadelphia Naval Shipyard that the NRL plant was considered “surplus to the needs of the Manhattan District.” “[T]he Commander Philadelphia Naval Shipyard is therefore authorized to proceed with the removal of subject facilities from the Naval Boiler & Turbine Laboratory and to dispose of the removed facilities,” either by declaring useful parts surplus, by returning them to the NRL, or by having them “jettisoned at sea”.

2. POSTWAR EFFORTS

Restarting the program