This paper explores the efforts and impact of the Society for the Diffusion of Useful Knowledge in China (1834–1839), which existed during the five years before the First Opium War. It contends that the Society represented a third form of British engagement with the Chinese, alongside the diplomatic attempts of 1793 and 1816, and the military conflict of 1839–1842. The Society waged an ‘information war’ to penetrate the information barrier that the Qing had established to contain European trade and missions. The foreigners in Canton believed they were barred from further access to China because the Chinese had no information on the true character of the Europeans. Thus, they prepared ‘intellectual artillery’ in the form of Chinese language publications, especially on world geography, to distribute among the Chinese, in the hope that this effort would familiarize the Chinese with the science and art of Westerners and thereby cultivate respect and a welcoming atmosphere. The war metaphor was conceived, and the information war was waged, in the periphery of the British informal empire in Canton, but it contributed to the conceptualization of war against China, both in Canton and in Britain, in the years before actual military action. Behind the rhetoric of war and knowledge diffusion in Canton, lay a convergence of interests between merchants and missionaries, which drove both to employ information and military power to further their shared aim of opening China up for trade and proselytizing. [ABSTRACT FROM PUBLISHER]