During the Cold War, the credibility of US nuclear weapons scientists was backed up by an integrated system for designing, testing, and manufacturing nuclear weapons. As the Cold War drew to a close in the 1990s, weapons scientists warned that their knowledge was so deeply embedded in the design and testing of nuclear weapons that it might not survive if this system were disrupted. Sociologists Donald MacKenzie and Graham Spinardi used this as evidence for the role of tacit knowledge in weapons design, suggesting that a halt to weapons design and testing could bring on a crisis of credibility, and possibly the ‘uninvention’ of nuclear weapons. In this paper, we examine how the weapons community has avoided such a crisis of credibility. Our analysis turns on the concept of sociotechnical repair – the processes communities and institutions engage in to sustain their existence, identity, and boundaries, particularly when faced with disruptive change. We examine two post-Cold War repair efforts that demonstrate how actors carefully balance discursive, institutional, and material change in the repair of complex sociotechnical systems. The Stockpile Stewardship Program positions weapons expertise as an abstract body of knowledge, and seeks to repair the credibility of weapons scientists by embedding their knowledge in a new sociotechnical context of computer simulation and experimental science. The Reliable Replacement Warhead concept emphasizes the close relationship between weapons knowledge and the design features of stockpile warheads, and seeks to repair credibility by introducing weapons designs optimized for long-term stockpile storage. These repair efforts show that weapons scientists’ views of their own knowledge continued to evolve after the end of the Cold War. In particular, weapons scientists maintained credibility with key constituencies by treating tacit knowledge as a flexible resource that can be successfully integrated into new sociotechnical arrangements.