plywood tunnel like an idled freight train that ran from concrete shields inside the Mike cab east to a bunker on Bogon, almost two miles away. This Krause-Ogle box, as it was called after its Los Alamos inventors, had to be elevated at the Bogon end to maintain a straight line of sight around the curvature of the earth. It was lined with polyethylene bags called ballonetts. Filled with helium from some twenty thousand two-hundred-pound bottles and with lead screens spaced along between bags for collimation, the tunnel ballonetts would pass gamma radiation and neutrons from the Mike explosion unattenuated by air to instruments on Bogon that would measure the timing of the Sausage's fission phase and the rise of the fusion reaction. The portholes that allowed the gammas and neutrons to pass into the Krause-Ogle box “probably diluted the shot,” comments Raemer Schreiber philosophically. “We wanted lots of data, but the portholes permitted energy to leak out that would otherwise propagate [the fusion reaction].” Since Los Alamos expected the Bogon bunker to be damaged, the instruments there were rigged to transmit their findings by radio in real time to another bunker a safe distance beyond; the box and its instrumentation would function even as the Mike fireball roared out from ground zero eating the long tunnel away.
The Sausage itself was instrumented heavily with built-in radio transmitters and exotic materials placed inside and near the device casing that would be radiation-activated and vaporized by the explosion and could be recovered as fallout by sniffer planes downwind. Seven large diagnostic pipes were welded to the Mike casing to isolate the moments when bomblight broke through the casing wall from successive points along the way down the cylinder, signaling the successful propagation of the reaction.
Mike assembly began in September 1952; by September 25 the complex secondary was complete and in position. Vacuum piping went on then and ACF engineers began installing the heavy outer casing. “I remember seeing the guys hammer the big, thick polyethylene plastic pieces inside the casing,” Harold Agnew recalls. “They hammered the plastic into the lead with copper nails.” Agnew, a tall, raw-boned Westerner, Colorado-born, had helped Fermi build the CP-1 reactor at the University of Chicago during the Second World War, had flown the Hiroshima mission with Luis Alvarez and would be Norris Bradbury's successor as director of Los Alamos. Fishing in his off hours at Eniwetok, Agnew caught a five-foot nurse shark. “We didn't know what to do with it, but Marshall Holloway hadn't been very collegial in managing the program. He tended to give orders without explaining why. So I put the shark in his bed. He never said anything, but after that he was much more collegial.”
Agnew was a member of the crew that would load the tritium into the Sausage's fission sparkplug, “a quite small amount,” says Carson Mark, “to strengthen the design, make things more certain, push them further in a favorable direction.” Agnew recalls that they carried the tritium out to Eniwetok ingeniously hydrided onto uranium:
We had steel buckets, maybe about three-eighths of an inch thick, with heaters built onto the outside. What you do is you cut uranium cubes, pure uranium metal, you put it in this thing, seal it all up and then you heat it real good. Then you cool it down and when you cool it down you activate it. We activated it first with just deuterium gas so that you get powdered uranium deuteride. The cubes turn into powder, probably black powder — I never looked at it, it's pyrophoric as hell.[48] Then you heat it again and drive off all the deuterium. Now you have a very active bed of uranium powder. Then when we put our tritium in it, it gobbled up the tritium and that's the way we transported it out.
To release the tritium from the uranium they plugged in the heaters on their uranium pots and drove off the gas into a gas bottle, just as they had done with the deuterium before.
If the deuterium for Mike was worth more than gold, the few grams of tritium were irreplaceable. Loading the exotic gas into the sparkplug, in the center of the complex secondary assembly, would be a delicate business. “You think about it,” Wechsler explains, “here's this thing down in the inside. You can't put a float in there or anything else to measure how much tritium you've bled in. So you set up to do a complete mass balance on how much tritium you have; by reading pressures each timed to a volume, you can tell how much mass you've shifted over. Then, as the pressure drops because the gas is condensing, you can add more. They knew just how much and they had so many uranium pots filled with tritium and they kept valving them in one at a time.”
Before loading the tritium, Agnew remembers, while the Mike secondary was still warm, “we decided we'd better do a dry run.” It almost came to disaster:
We couldn't use tritium because we didn't have very much, so we said, we'll use deuterium because that wouldn't contaminate our lines. So we put the stuff in and watched to make sure we didn't have any leaks. Slowly — My God, there it was, how can we have a leak? Thought, thought and thought and then somebody said, maybe it's hydriding. Because we were putting this deuterium onto warm uranium and it was a slow leak but it was a leak. Well, what are we going to do? Of course we talked with Carson [Mark] and Marshall [Holloway]. We were worried we'd used that amount of deuterium and hydrided it, but hell, that's not going to bother anything. So we said now we'd use an inert gas. I don't remember whether we used argon or helium, but it didn't leak. So the deuterium was hydriding. But we were really upset — there was no way we could have fixed a leak because [the sparkplug] was way in the middle of the [secondary], which had been built up piece by piece by piece.
Agnew also worried about soldiers standing around Elugelab guarding the Mike shot cab with guns. “Sort of drove us bananas, all this liquid deuterium around. I was worried that some nut would shoot and actually hit the bomb. So a couple of us raised hell and got them out. Who's going to invade the island?”
On October 3, the British saluted
Practice cryogenic cool-downs with liquid hydrogen started on Mike on October 10. The Navy barged Wechsler's dewars over to Elugelab to deliver the cryogenic liquids and serve for storage. Final filling with liquid deuterium began in the evening on Sunday, October 26. Air froze solid in one of the deuterium lines and had to be removed; otherwise the filling was routine. A stretch of bad weather began the next day, worrying everyone up to the end of the month and grounding the inter-island fixed-wing airlift service. Fortunately, the task force had mustered enough helicopters to substitute for the grounded aircraft.
A new core for the TX–V fission primary arrived by C-124 cargo plane from Los Alamos a few days before the target date. As Agnew remembers it, Marshall Rosenbluth initiated the idea of changing the core of the Sausage primary:
Marshall may have saved the Mike shot. The nice thing about being overseas was that they fed you very well. They understood that if you want to have happy guys, you ration the booze — a fifth a week or something like that — but you serve very good food: shrimp, steak. Just really good food because you've got all these construction guys. You have movies and food. That's it. Ice cream, lots of ice cream. One night they had shrimp and Marshall ate too much. He couldn't sleep, and he got to thinking about what was going to happen and he decided the core we were using was prone to preinitiate and that we should change the core. He talked with Carson, I guess, and indeed there were rapid renegotiations.
The bellyache that saved the shot must have happened in August, when Mark says discussions of the core change began, “to decrease the chance that the core would predetonate and fail to deliver the proper yield.” The substitute core, a levitated composite model built at Los Alamos, contained more uranium and less plutonium than the one it replaced. It would be less likely to chain-react before it reached maximum compression and would therefore react more efficiently, delivering more X-radiation to the secondary than the suspect core might have done.
Estimates of Mike's yield ranged so wide that the entire land task force had to be evacuated from the atoll onto ships, a tour de force of logistics. People packed up and went to sea whenever they finished their assigned preparation work. The scientists would be the last to go because they wanted to leave the Mike instrumentation unattended as briefly as possible. The last to leave would be the arming team, part of the firing party on the USS
