Most cyber intrusions are a form of intelligence rather than warfare, but intelligence remains undertheorized in international relations (IR). This article develops a theory of intelligence performance at the operational level, which is where technology is most likely to affect broader political and military outcomes. It uses the pragmatic method of abduction to bootstrap general theory from the historical case of Bletchley Park in World War II. This critical case of computationally enabled signals intelligence anticipates important later developments in cybersecurity. Bletchley Park was uncommonly successful due to four conditions drawn from contemporary practice of cryptography: radio networks provided connectivity; German targets created vulnerability; Britain invested in bureaucratic organization; and British personnel exercised discretion. The method of abduction is used to ground these particular conditions in IR theory, revisit the evaluation of the case, and consider historical disanalogies. The result is a more generalizable theory that can be applied to modern cybersecurity as well as traditional espionage. The overarching theme is that intelligence performance in any era depends on institutional context more than technological sophistication. The political distinctiveness of intelligence practice, in contrast to war or coercive diplomacy, is deceptive competition between rival institutions in a cooperatively constituted institutional environment. Because cyberspace is highly institutionalized, furthermore, intelligence contests become pervasive in cyberspace.