Operation Sundial: The Terrifying 10-Gigaton Nuclear Weapon That (Thankfully) Never Was

But while the bombs that were dropped on the two Japanese cities at the end of the Second World War were hideously powerful (the bomb dropped on Hiroshima was 16 kt of TNT, while the one dropped on Nagasaki was 21 kt), they were nothing compared to the biggest bomb that was ever detonated. 

This title goes to the terrifying “Tsar Bomba”, tested by the Soviet Union on October 30, 1961, which was designed to have the maximum explosive yield of 100 million tons (100 megatons) but was only detonated with 50 megatons. This was over 3,300 times more powerful than the bomb used at Hiroshima, which killed 140,000 people. Imagine what would have happened had this weapon been used in a conflict.

As you can probably tell from my language, I’m setting the story up for a “but” moment, and it really is going to be a kicker.  

If someone were to use a weapon equal to the Tsar Bomba’s yield on a city today, the devastation it would cause would be unthinkable. This is especially the case as the test weapon is 40 times stronger than the largest nuclear weapon owned by the United States today. It was a monster. 

But…while the Tsar Bomba may be the largest nuclear weapon ever tested, there was one project carried out in the United States that, had it come to fruition, would have created something that dwarfed even this titan of killing potential. The outcomes of Operation Sundial are both a lesson in how human imagination, the terrible logic of Cold War political posturing, nationalism, and technological aspiration can create something truly terrifying.

Destructive speculation

The nuclear weapons detonated in Hiroshima and Nagasaki were examples of fission weapons, which means they gained their explosive power from a chain reaction produced when heavy atomic nuclei (from the enriched uranium isotope uranium-235, or isotope plutonium-239) were split (fission) to release immense energy. 

The principle was put into effect during the now famous Trinity Test that took place in the New Mexico Desert in July 1945. Although the explosion produced at this event was incredible, there were already some researchers who were imagining ways to make even bigger booms. 

Instead of fission, the “super” weapons would have relied on fusion reactions, whereby two light atomic nuclei are combined to form a heavier nucleus, a process that releases even larger amounts of energy. However, this type of reaction is difficult to achieve, requiring a two-stage approach whereby the energy produced by a fission explosion is used to power a fusion reaction using deuterium and tritium, two heavy hydrogen isotopes. 

The technology for these weapons, known as hydrogen bombs (H-bombs) or thermonuclear weapons, was not available to scientists at this point, so they remained the products of deadly speculation… at least for a few more years. 

By the start of the next decade, the situation had changed quite a bit. The Soviet Union tested its own nuclear weapon in late August 1949, ending the US’s monopoly on the bomb and signaling the start of a new arms race. 

The anxiety caused by this event, coupled with the communist takeover of China in the same year, intensified the need for the US to have a “superbomb” to counter the threats in the increasingly destabilized world it perceived. As a result, the US National Security Council released a secret policy paper in 1950 that called for four times the defense spending to address this problem. 

In late 1950 and 1951, Stanislaw Ulam and Edward Teller, two scientists who had worked on the Manhattan Project, started to propose real ideas for the first two-stage nuclear weapons. They eventually produced what is known as the Teller-Ulam design (sometimes the Teller-Ulam configuration), which underpins the concepts for thermonuclear weapons today. 

Then, on November 1,1952, the US tested its first fusion weapon, the H-bomb codenamed “Mike”, during Operation Ivy at Enewetak Atoll in the Marshall Islands. This weapon was the first demonstration of this type of multi-megaton thermonuclear weapon that had been dreamed up by scientists, like Teller and Ulam, since the 1940s. Mike’s explosive power made its predecessors look like fireworks in comparison; it achieved a yield of 10.4 megatons – 500 times larger than the bomb dropped on Nagasaki. Its detonation created a crater that was 1,900 meters (6,240 feet) in diameter and 50 meters (164 feet) deep. But this was not enough.

The success of Mike was later followed by a more compact weapon test, known as “Shrimp”, which was detonated in 1954 and produced a much larger yield than expected. Not only were the scientists caught off guard by the power of this 15-megaton explosion – 1,000 times more powerful than the bomb dropped on Hiroshima – they were also shocked by the amount of radioactive fallout it produced. And yet, even this was not enough; Teller wanted more. 

Sundial in all its terror 

Much about Project Sundial remains classified today, but we know enough about it to know it was a crazy idea that would have had global implications if it had ever been realized. 

The project was masterminded by Teller and colleagues at the University of California Radiation Laboratory’s Livermore Branch and sought to create weapons not in the kiloton or megaton range, but in the gigaton range. The two weapons designed for this purpose were known as Gnomon and Sundial. The former was envisioned as a primary for the latter, delivering a 1,000-megaton detonation to produce a fusion reaction in the latter that would achieve a 10-gigaton (10,000-megaton) explosion – 200 times more powerful than the Tsar Bomba mentioned in the introduction.

It might be tempting to dismiss this as crazed imagination, a case of scientific speculation that never turned into anything real, but it seems Teller and colleagues took it seriously. For several years, as the Bulletin of the Atomic Scientists has shown, researchers worked on Gnomon and intended to test a prototype in Operation Redwing in 1956, which thankfully never took place. 

“It is hard to convey the damage of a gigaton bomb, because at such yields many traditional scaling laws do not work (the bomb blows a hole in the atmosphere, essentially)”, the Bulletin explains.

The sheer destructive power of this weapon would have had severe consequences for the planet. To put this into perspective, the detonation of a weapon equivalent to Sundial at 45 kilometers (28 miles) above the Earth could set fires over an area about the size of France. If the bomb dropped on Hiroshima killed 140,000 people, and this explosion was little more than a nuclear hiccough compared to the power of Sundial, then imagine the death toll it would have had.