The nuclear engineer emerged as a new form of recognised technical professional between 1940 and the early 1960s as nuclear fission, the chain reaction and their applications were explored. The institutionalization of nuclear engineering--channelled into new national laboratories and corporate design offices during the decade after the war, and hurried into academic venues thereafter--proved unusually dependent on government definition and support. This paper contrasts the distinct histories of the new discipline in the USA and UK (and, more briefly, Canada). In the segregated and influential environments of institutional laboratories and factories, historical actors such as physicist Walter Zinn in the USA and industrial chemist Christopher Hinton in the UK proved influential in shaping the roles and perceptions of nuclear specialists. More broadly, I argue that the State-managed implantation of the new subject within further and higher education curricula was shaped strongly by distinct political and economic contexts in which secrecy, postwar prestige and differing industrial cultures were decisive factors.