In the span of the first few years after Japan’s defeat in World War II, five of Japan’s leading earth scientists came forward to warn the nation that major earthquakes would soon occur. They (almost) never did. This article focuses on those predictions to highlight the debates that shaped early postwar efforts in Japan to make scientists, and earth scientists in particular, guardians of the public’s safety. It draws on multiple archival collections, participant accounts and popular media coverage to explore the tensions between individual scientists and newly formed, officially sanctioned bodies charged with coordinating earthquake prediction research. These tensions, I argue, reflect both a long-standing ambivalence within the field toward prediction’s legitimacy, and the emergence of a new set of research and policy imperatives for Japan’s earth scientists that privileged it. The legacies of the Occupation-era encounters with prediction include the 1962 publication of Earthquake Prediction: Current Status and a Plan for Development, the formation of the Coordinating Committee for Earthquake Prediction in 1969 and the passage of the Large-Scale Earthquake Countermeasures Act in 1978.