On October 18, 1961, AEC Chairman Glenn Seaborg wrote a memo to President Kennedy outlining the possibilities. A 100-megaton bomb, he explained, would weigh about 30,000 pounds and would be 6 feet in diameter and 12 feet in length. A 50-megaton bomb might be smaller but would still be extremely heavy (between 20,000 and 25,000 pounds). If this effort was given the “highest priority,” they could have such a weapon in the US stockpile within six months to a year, but such an effort would interfere with other programs. A test would be necessary to ensure reliability, but this could be done at reduced yield (no more than 10 megatons). The AEC had no reason to believe, he concluded, that the Soviet Union could not deliver their own such weapons to American targets.
A few days later, Seaborg met with weapons scientists to discuss building high-yield weapons. Betts initiated a discussion with Sandia National Laboratory over the feasibility of dropping weapons with yields of 30 or 50 megatons from a B-52, which would require using drogue parachutes to ensure the survival of the pilots. At the same time, a team of Livermore scientists got together to review the possibilities of a US return to nuclear testing. Along with ideas relating to more optimized designs and “clean” bombs deriving most of their yield from fusion, they were intrigued once again by Teller’s possibility of bigger bangs: “USSR high-yield tests have reawakened interest in high-yield testing by the United States. High-yield weapons (50 megatons to 1,000 megatons) should be reconsidered and re-evaluated for their possible military use.” Again, let that sink in: Even after denouncing the Tsar Bomba as pointless terrorism, there were scientists and military planners working for the US government who were considering nuclear weapons with yields 20 times larger.
In early 1962, one scientist at the Sandia lab reported to his colleagues about this sudden interest in superbombs, noting dryly that the Soviet detonation had “started some thinking in this country that there must be a good application for these things that has escaped our attention… the military would like to see the development of a few [very high-yield] bombs and would even feel good if a few were in the stockpile even though no known targets justify such weapons.”
Over the course of late 1961 through 1962, the United States itself engaged in a series of vigorous nuclear weapons tests. The first set, Operation Nougat (September 1961–June 1962), was underground at the Nevada Test Site, and featured only low-yield detonations (these were the tests that Kennedy had worried would be perceived as too small). The second, Operation Dominic (April 1962–October 1962) was a rapid series of over 30 nuclear detonations at Johnston Atoll and Kiribati in the Pacific Ocean. Dominic was the first series of atmospheric testing done by the United States since the end of the moratorium, and it involved a variety of activities, including testing new weapons concepts, detonating weapons in outer space, probing the electromagnetic pulse effect, and detonating the first fully “mated” system of a nuclear warhead and a launched missile.
While most of the Dominic tests were in the kiloton range, a few were megaton tests. Only one crept up to around 10 megatons; the United States prided itself, in press releases, on testing its warheads at less-than-full yield, to reduce fallout in the atmosphere. (The entire Dominic test series was about 40 megatons, less than the single Tsar Bomba shot.) Even though it does not appear that any of the Dominic shots were aimed at developing a 100-megaton bomb, several of the new designs did play key roles in the AEC’s thinking about “very high-yield” weapons. Notably, three of the tests were for a new, “revolutionary” weapons concept known as RIPPLE, developed at Livermore by weapons designer John Nuckolls. The details of RIPPLE are still classified, but it promised to get very high fusion yields out of relatively light packages by dramatically optimizing how the weapon produced nuclear fusion reactions.
The vigorous 1962 testing series, and the barely avoided catastrophe of the Cuban Missile Crisis, appear to have put a damper on these discussions temporarily. But by December, AEC Chairman Glenn Seaborg reported to the Secretary of Defense, Robert McNamara, that the AEC was prepared to develop an American Tsar Bomba if ordered to. Seaborg divided the possibilities into three categories. The first was to scale up existing weapons, like the Mark 41, to higher yields. This would be very quick, but the weapons would be extremely bulky. The second option was to use the new RIPPLE concept, which would get lighter weights but place unusual constraints on volume (probably because the secondary in a high-yield RIPPLE device would be spherical). Finally, there were weapons concepts “yet to be proven feasible” that would potentially achieve “the ultimate high yield, low weight, and acceptable volumes.” The AEC noted it would be possible—by diverting significant laboratory resources—to have devices ready to test by the end of 1963.
Much of the memo quoted above is still classified (though many versions of it exist, and some are less redacted than others), but there is one copy that contains some relevant technical information. Los Alamos had reported to Seaborg that they would be able within three years to build a 100-megaton bomb (of which some 20 to 30 megatons would be from fission, but “clean” options could be made as well) that would weigh 30,000 pounds and would be 23 feet long, with a diameter of 5.5 feet. Livermore claimed it could scale up a Mark 41 to high yields and have it weigh only 20,000 pounds, and it would only take one year. But Seaborg again cautioned that to pull any of this off would require a substantial investment of time and resources, and he would not do it without explicit direction from the president: “to produce high-yield weapons will require a scope of effort much larger than any previous AEC weaponization effort.”