Logistic and personnel requirements were in proportion. Every pair of vacuum tanks required an individual operator seated at a console, continually adjusting the current to focus the beam. An army of technicians was needed to monitor the orange uranium-oxide “feed” material for the beam and later scrape the errant green “gunk”—uranium salts dissolved in carbon tetrachloride—from the insides of each tank. An army of chemists would separate out the silvery powder containing U-235 that was left in the receivers following each weeklong run.
Initial guesses were that 2,500 people would be necessary to operate the production plant; by spring 1943 that estimate had already swelled to 13,500.8 (A year hence it would exceed 25,000.) But the shortage of technicians turned out not to be the problem that Lawrence had anticipated: unskilled workers—mostly young women, recruited from the Tennessee hills—proved at least as adept at running the Calutrons as degree-bearing physicists, and posed less of a security concern for the army.9
Meanwhile, the output of Berkeley’s scale-model Calutron was still meager at best. By mid-April, following its first full week’s run, the machine had produced just under 4 grams of uranium metal, enriched to an average of 20 percent U-235. The “great optimism” that the boys had heard Lawrence express hardly seemed warranted. The beam had actually been too intense, eating its way through the receivers, and many vacuum tubes had burned out. “We’ve got to get the wrinkles out as soon as possible,” Ernest needlessly admonished the boys.
But the results two weeks later seemed more dismal than ever. One vacuum tank had worked for only three days, whereas shorts and leaks had prevented a second tank from operating at all. Nonetheless, Ernest assured Groves—as he had Oppie—that the goal of 1 gram of U-235 per day was now in sight. “The thing that interests me,” the general replied gruffly, “is where do we go from here.”10
Groves had already decided that the fifth racetrack, still under construction, would be modified to become the first Alpha II Calutron. After Oppenheimer reported from Los Alamos that the gun-type bomb might require three times the amount of uranium originally estimated, Lawrence launched a campaign to double the number of Calutrons. Consideration was given to tearing down all the Alpha I racetracks and converting them to the new, four-beam Alpha II design.
Groves also authorized the building of two additional Beta units to process the expected additional output from the Alpha IIs—even though, as Lawrence pointed out, the design of the Betas remained unproven; not even a prototype had yet been tested.11 The first full-scale Calutron was scheduled to go into operation that fall. On November 4, 1943, Lawrence reminded the Coordinating Committee that the “zero hour is approaching.”12
* * *
Following the alert sounded by Hoover, bureau agents had fanned out from FBI field offices that summer, looking for instances of Communists contacting scientists about a vital but unspecified secret project. Except for San Francisco, the dragnet yielded few suspects. FBI agents at the El Paso, Texas, office reported that efforts to “‘shake down’” scientists arriving at Los Alamos had been frustrated by the wartime housing shortage: Oppenheimer was quartering new arrivals in guest ranches dispersed throughout the area.13 A mail cover on letters going into and out of the lab was begun instead.
Agents in Santa Fe, shadowing a Russian-born man and wife who had recently moved to the city, described the couple as “a trifle Bohemian in their outlook” and reported that “their principle [sic] activity seemed to be drinking.”14 Other FBI agents tailed a Russian-born illustrator of children’s books traveling by train from New York all the way to his home in New Mexico. A search of his luggage turned up playing cards, an address book, and The Tall Book of Mother Goose.
In San Francisco, Pieper was becoming increasingly exasperated both with his assignment and with Pash. The FBI man wrote Hoover complaining that his agents would be able to do a better job if they knew what they were looking for. But the army still stubbornly refused to publicly acknowledge its involvement in the project at Berkeley, although it was hardly a secret on campus. Pieper was also distraught about security at the Rad Lab—where “rejected material” was simply thrown into garbage cans in a public area, he noted—and contemptuous of the tradecraft practiced by his allies in the battle, the G-2 agents that the bureau knew as “creeps.”15
In late July, Pieper informed Hoover of the latest idea hatched by his nemesis:
Pash has been negotiating for authority from Washington to obtain a boat for the purpose of Shanghaiing various Communists employed in the Laboratory and taking them all out to sea where they would be thoroughly questioned “after the Russian manner.” (Blank) stated that he realized any statements so obtained could not be used in prosecution but apparently Pash did not intend to have anyone available for prosecution after questioning.16
Pieper dissuaded Pash from carrying out this or his backup plan, which was to take Weinberg to a San Francisco hotel and interrogate him with the idea of “turning” the physicist into a double agent.17 Fearful that the army’s actions might have already tipped the spy suspects off to COMRAP’s wiretaps, Pieper advised his boss: “Pressure was brought to bear to discourage this particular activity.”18
* * *
Groves considered Soviet espionage at the Radiation Laboratory a serious enough matter to bring it before the Top Policy Group at a meeting in Washington on August 17, 1943. Following a progress report on the bomb project, Groves summarized the status of the army’s investigation into what he called the “California trouble,” including the Nelson-Joe conversation and Nelson’s subsequent meetings with Ivanov and Zubilin.19
That same day, Groves had Lansdale hand-deliver a note to Secretary of War Stimson with an attached draft memorandum for the president. “It is essential that action be taken to remove the influence of FAECT from the Radiation Laboratory,” the memo
