It is now common in the study of concentrations of industry to consider them as local or regional clusters of firms. This stems from a wave of empirical and theoretical research into concentrations of economic activity continuing the earlier work of Alfred Marshall who observed that firms seemed to accrue benefits from concentrating in space and time. By 1914 the city of Coventry was undergoing rapid expansion and embracing a second wave of British industrialisation with its economy comprising a series of clustered light-engineering firms at the heart of cycle, motorcycle and motor vehicle production. During the First World War, the city became transformed into an arsenal of war for four-and-a-half years and contributed greatly to British and Allied armaments and munitions production. Crucially, the research conceptualizes this collection of firms as an evolving armaments and munitions cluster, undergoing rapid expansion and adaptation to meet the demands of the war effort. The research identifies the principal characteristics of no less than 166 factories manufacturing armaments and munitions and 13 support institutions and infrastructure and maps their changing distribution across Coventry between 1914 and 1918. Secondly, the research identifies the type(s) of cluster this wartime economy became and shows the cluster grew from a predominantly nucleated hub-and-spoke cluster to a state anchored/centred cluster and finally to a cluster leading to innovation. Thirdly, the research reveals how under wartime conditions a cluster was able to evolve rapidly from one type to another by demonstrating it was through the Coventry Armaments Output Committee. Finally, these research findings are related to what impact, both positive and negative, a successful WWI armaments and munitions cluster had upon the city’s development, suggesting engineering science and inter-firm and inter-governmental co-operation, were two important legacies.