Fogbank: how the United States forgot how to make its nuclear weapons

If you happened to scan a map of Tennessee in the early 1940s, your finger would inevitably pause over the recognisable urban centres of Memphis, Nashville or Knoxville. A seemingly unremarkable settlement of Oak Ridge, situated 40km west of the latter, probably wouldn’t catch your attention – indeed, depending on how detailed your map is, it might not be marked at all. This obscurity suited one organisation down to the ground – The United States government, for whom the town had played a major, some might even argue existential, role in the fate of the country since its incorporation in 1942.

If you lived in Oak Ridge in the years that followed its foundation, a normal day would involve all the recognisable mundanities of any unremarkable American township – you might wander down your front path and check for any mail before quickly polishing off a cup of coffee and perhaps some oatmeal before heading off for a day’s work. Work, though, is a strange experience. You not only don’t really understand what your job is, but you also don’t know who you work for or who your colleagues are. Your work is also curiously simple and monotonous. Your entire remit might, for example, consist of spending an entire day watching a dial and listening out for a changes in a incessant crackling sound. If the dial span too far to the right or the crackle grew more aggressive, you would alert your supervisor. You don’t know what the dial indicates or what is causing the crackling you are monitoring. You don’t know what the supervisor goes away and does with the information you pass to them and you are not allowed to ask. This the totality of your working day and every day is the same. You are desperate to know exactly what you are doing, but the job pays well and life in Oak Ridge is good, so you bury your curiosity and get on with it.

All across town, people are carrying out a huge variety of similarly mundane tasks, unable to compare or speculate about what they are all a part of. What they don’t know is that the land on which their small town sits was specifically identified by the United States government for a specific purpose: Oak Ridge was one of the 19 production sites for the Manhattan Project, which led to the manufacture of the first nuclear weapons – specifically those dropped on Hiroshima and Nagasaki to end Japan’s involvement in the Second World War¹. Chosen for the combination of it rural location and small population, but good transport links and plentiful access to fresh water and energy, Oak Ridge was home to several laboratories and manufacturing plants.  These were filled not only with some of the country’s top scientists and engineers, but also thousands of residents carrying out their monotonous tasks, completely unaware that they were contributing to the development of some of the most devastating weapons ever conceived. As far as the government was concerned, the fewer people knew what they were doing, the less potential there was for the top-secret operation to be uncovered.

Oak Ridge would continue at the centre of the development of the United States’ nuclear arsenal for decades after the end of the Second World War and science and technology continue to play a crucial role in the economy and culture of the city in the modern day. Though the origin of Oak Ridge is a fascinating one, this story is concerned with the development of nuclear weapons at Oak Ridge in the proceeding decades and specifically begins in 1975. At this time, engineers at Oak Ridge were tasked with building W76 warheads. These conical objects, roughly 2 feet or 60 cm in length, are loaded onto ballistic missiles typically launched from submarines. These warheads flowed out of Facility 9404-11 of the Y-12 National Security Complex until 1989². Four years after the final W76 left the facility, it was slated for decommission and by the end of the 20^th century, only a skeleton operation remained at the site for small-scale testing purposes. The role played by this specific laboratory at Oak Ridge was not thought about again until 2000, when the decision was taken to refurbish the existing arsenal of nuclear warheads manufactured in preceding decades. This was a common practice – replacing old warheads is expensive, time consuming and potentially dangerous – but there was just one problem: no one could remember how they were manufactured.

Many of the scientists and engineers who originally worked on the project were either retired or had died and there existed very few written records, perhaps due to the significant secrecy that veiled all nuclear weapon development. The problem centred around a mysterious object called Fogbank. To this day, we cannot be sure exactly what Fogbank does; Dennis Ruddy, former General Manager at Oak Ridge, has said the following about its role in function of nuclear weapons:

“The material is classified. Its composition is classified. Its use in the weapon is classified and the process [of its manufacture] is classified.”³

Despite Dennis Ruddy’s illuminating description, some believe that they have pieced together a fairly accurate picture of Fogbank’s function. It is thought to be an aerogel, a fascinating material in which the liquid component of a gel is replaced with a gas. Aerogels are described as feeling like polystyrene but looking like smoke⁴ and have some remarkable physical properties, including substantial conductivity of heat. It is their remarkable thermal conductivity that makes them such a useful component of modern nuclear weaponry.

The earliest nuclear weapons, such as those dropped on Hiroshima and Nagasaki in 1945, were fission bombs. The devastating power of these weapons is derived from the energy that is released when an element is forcibly split into two smaller elements. The blasts can be so devastating because these fission reactions are exponential in nature, meaning the system grows and grows in power⁵. The energy released from each fission event accumulates to become the terrifyingly powerful blasts that caused such devastation on those fateful days in 1945.

Modern nuclear weapons, however, are referred to as H (Hydrogen)-bombs or thermonuclear bombs. These also harness the energy released when atoms interact with each other. Unlike their predecessors, however, these weapons derive their power from the energy released when two elements fuse together to form a larger one. It is in these H-bombs that aerogels such as Fogbank are thought to play a crucial role. Most conventional H-bombs contain both a small primary fission bomb and a secondary fuel which allows the significantly more powerful fusion processes to take place. The ignition of the fission fuel releases powerful x-rays, which irradiate the aerogel suspension in which the fusion fuel sits. The aerogel then becomes a superheated plasma, a state of matter in which atomic particles are moving with so much energy that electrons are ripped away from their nuclei. The superheated plasma compresses the secondary fusion fuel, in effect transferring the energy generated by the initial fission reaction⁵. This role in sparking the fusion reaction responsible for the explosive power of the weapon means materials such as Fogbank are referred to as ‘Interstage Materials’ and are thought to be crucial to the function of nuclear weapons.

If this is indeed the role played by Fogbank, then replacing it would have certainly been on the checklists of the engineers responsible for refurbishing the existing nuclear arsenal in Oak Ridge in 2000. Nuclear fuel could easily be replenished, rusting metal plating was easily fitted, but it was Fogbank at the centre of their embarrassing conundrum – it was the interstage material that no one knew how to manufacture. The National Nuclear Security Agency (NNSA) held a nonchalant position: if the material had been created at the site decades earlier, then it would be a simple job to do it again. Since the computer simulations at the time were also not capable of highlighting a viable alternative, the NNSA directed the engineers and scientists at their disposal to simply reverse engineer the Fogbank samples they still had. However, it wasn’t quite that simple. Despite no expense being spared on brand new facilities – the initial costs spiralled to over $23 million – engineers just couldn’t produce Fogbank that worked as effectively as the decades-old samples. Each step of the labour-intensive manufacturing process was painstakingly poured over and machinery was constantly cleaned to eliminate any risk of impurities being introduced into the samples.

It took until March 2007, and a further $69 million of public funding, to reach a breakthrough. In most laboratories, every step is taken to produce a pure product – impurities inevitably reduce its effectiveness. As it transpired, this was not the case for Fogbank. A specific impurity led to a subtle change in the structure of the final product which was crucial to its function⁶. By using modern, state-of-the-art facilities and introducing aggressive cleaning measures, engineers were removing the very impurities that were at the heart of their frustrations. By specifically introducing the essential impurity at the appropriate step in the manufacturing process, engineers were finally able to deliver fully refurbished warheads, albeit years behind schedule and at a cost approaching $100 million, which will be operational until well into the 2040s.

The Fogbank story is an example of lost knowledge. Sometimes this concept is a natural result of societal progression and does not have any detrimental effects: we do not lament the fact that no one can precisely describe how to hunt a mammoth or repair a hand-cranked car engine. Lost knowledge can, however, be a serious issue. By relentlessly pursuing the latest and greatest technologies and in doing so earmarking previous discoveries and customs to be left in the past, we may be losing vital knowledge that may be required some way down the line. NASA experienced this first hand in the early 21^st century, when then President George Bush Jr. expressed a desire to return astronauts to the moon. Without the budget to build new space shuttles, NASA were faced with the need to refurbish their aged fleet. To do so they needed specific computer chips manufactured by Intel when the shuttles were developed decades earlier; they couldn’t simply slot modern technology into older systems. With Intel having long destroyed its stockpile of such ancient chips, entire departments of NASA were created to scour internet marketplaces such as eBay for individuals and companies looking to make a quick buck from computers that had been gathering dust in cellars around the world to scrape together enough chips for their renewed space programme⁷.

Lost knowledge isn’t something that is reserved for the modern era. In 1901, divers off the coast of the Greek island of Antikythera discovered a curious object aboard a Roman-era shipwreck. In the century that followed, experts determined that they were looking at possibly the first known analogue computer. The complicated machinery contained within the object, known as the Antikythera device, was capable of modelling the movement of the five known planets and predicting astronomical events such as eclipses⁸. The device showed remarkable knowledge, precision and craftsmanship and has variously been dated between 204 BC and 87 BC by different sources. It was of such quality that machines with a similar level did not appear for another 1,500 years. We can never know how different our understanding of the universe may have been if the Ancient Hellenic advances behind the Antikythera device were sustained in the centuries that followed.

Science and technology will always move forwards. It is right that scientists and engineers seek new knowledge and create new products that improve our lives or our understanding of the world around us. In doing so, however, we must not forget what brought us to this point – we can never know when we might need to rely on the work of those who came before.