When war broke out in 1914, both sides initiated elaborate efforts to shift the world economy to a war footing. The war divided trade partners and exposed dependence on imports of strategic materials, prompting efforts to exploit enemies’ commercial vulnerabilities through the tools of blockade and submarine warfare. As the belligerents struggled to secure their supply lines, they also began to devise new legal and institutional safeguards to ensure permanent access to strategic materials in peacetime. Lucien Coquet, Hubert Llewellyn Smith, Bernhard Harms, and Richard Riedl participated in the operation of the war economy and helped initiate planning for the future transition from war to peace. Their stories show how the experience of economic warfare was framed by the trade institutions and information networks inherited from the belle époque.