What we do know is that it’s immensely complicated to make and has to be purified using a dangerously volatile chemical.
To this day, details about the weapons in America’s nuclear arsenal, especially regarding their warheads, remain some of the most secretive, while still publically known, elements America’s nuclear weapons enterprise. There is no better single example of this than a material that the U.S. Department of Energy has used to build thermonuclear warheads, also known as hydrogen bombs, that is so secret that no one knows exactly what it does or exactly what it’s made of, and that is only ever referred to publicly by a codename, Fogbank.
Fogbank first gained relatively widespread public attention between 2007 and 2008 as it emerged that the material was at the root of technical delays in the life extension program for the W76 warhead. The W76 series is employed on Trident II submarine-launched ballistic missiles, also known as Trident D5s, in service with both the U.S. Navy and U.K. Royal Navy. The National Nuclear Security Administration delivered the last life-extended W76-1 warheads in 2018.
“There is a material that we currently use and it’s in a facility that we built … at Y-12,” then-NNSA director Thomas D’Agostino told members of the House of Representatives in 2007, referring to the Y-12 National Security Complex, a nuclear weapons production facility located near the Oak Ridge National Laboratory in Tennessee. “It’s a very complicated material that – call it the Fogbank. That’s not classified, but it’s a material that’s very important to, you know, our [W76] life extension activity.”