This article shows how cultural-historical methods can illuminate otherwise opaque aspects of the relationship between war and technological change. In particular, it examines the early history of radio at the time of the South African War when Guglielmo Marconi battled a range of rival inventors and entrepreneurs in the British public sphere. The author argues that although the technology was not sophisticated enough to fulfill many actual military needs, the contemporary preoccupation with "security," which was expressed in a range of cultural, political, and economic registers, continued to shape understandings of radio's ideal uses. As a result, rather than develop its potential as a mass medium in an era that saw the flourishing of such media, scientists and inventors persisted in developing radio into an instrument of long-distance, point-to-point communication, for which it was arguably much less technically suited at the time.