One of the most dominant security issues of twenty-first century has been the u.s. led battle against transnational terrorism—the aptly named Long War. Over the past fifteen years the Long War has been examined using multiple perspectives; however, one central mechanism is missing in current analyses: defence diplomacy. Defence diplomacy enhances the diplomatic and security capacity of a state, providing the only link between executive office and the ministries of foreign affairs and defence, two vital institutions in the Long War. Using a case study of u.s. defence diplomacy in Afghanistan from 2001–2014, the paper argues simply that the practice of defence diplomacy far outweighs current theories on what it is, how it works and why it matters? The paper aims to generate a more nuanced understanding of defence diplomacy, as well as identifying it as a key component of the u.s. ct/coin strategy to achieve its Long War policy objectives.