On February 17, the Navy took delivery of its first refurbished W76 warhead. The W76 is a nuclear payload that sits atop the Trident II missiles carried by America's Ohio-class submarines. As such, it represents an important part of the country's nuclear arsenal. The refurbishment of the aging W76s has taken much longer than was originally anticipated because once the engineers cracked open the old warheads they encountered a substance codenamed "Fogbank." And they had no idea how to replicate it.

The mystery of Fogbank begins in the late 1970s, in a building called Facility 9404-11 on the grounds of the Y-12 complex in Oak Ridge, Tennessee. The Oak Ridge site sprang from the original Manhattan Project and became one of the seven facilities making up America's nuclear weapons complex (an ominous-sounding phrase coined by the government, and gleefully seized on by the antinuclear left).

Most everything about Fogbank is classified, but we know from unclassified official sources that Fogbank was manufactured in Facility 9404-11 from 1975 until 1989, when the final batch of W76s were completed. After that, the building went dormant. By 1993 it was slated for decommissioning, leaving behind only a pilot plant which had been used to produce small batches of Fogbank for test purposes.

But warheads, like other materiel, have operational lifespans. In 1996, the government realized that large parts of its nuclear arsenal would need to be replaced, refurbished, or pulled from service. In response, the Department of Energy initiated a refurbishing program with the goal of

Straight away, the NNSA realized that Fogbank could be a problem because, as the GAO would later report, they had "kept few records of the process when the material was made in the 1980s and almost all the staff with expertise on production had retired or left the agency." The NNSA briefly considered creating a substitute for Fogbank, but ultimately decided that since they had made it before, they would be able to make it again.

But Fogbank proved to be quite tricky. With Facility 9404-11 gone, a new production house was required. There were delays with the construction, and frustrated engineers kept failing to produce a usable version of the mysterious substance. As deadlines passed and the schedule was pushed back again and again, the NNSA eventually decided that, come to think of it, they would invest $23 million in an attempt to find a Fogbank alternative.

As it happens, in March 2007, the engineers found some success and came up with a tentative process for making Fogbank. But when the final tests were run, the material had problems. In September 2007, the NNSA upped the Fogbank project to "Code Blue" status, making it a major priority of the agency. That effort failed, too.

A year later--and with an additional $69 million spent--the NNSA finally rediscovered a workable way to manufacture Fogbank. And seven months after that, the first refurbed warhead was finally handed over to the Navy, nearly a decade after the government began the life-extension program. The NNSA charmingly refers to the ordeal as an example of "lost knowledge."