Historians in recent years have begun examining how relationships between locales in different nations have shaped scientific communities, identities, and research. Using such studies as a springboard, this paper considers the origins and assumptions of a transnational collaboration in basic and applied research that formed among Anglo-American physiologists during the Second World War. At that time, physiologists on both sides of the Atlantic created a powerful network focused on questions of joint defence. Including such figures as E. D. Adrian, John F. Fulton, Detlev Bronk, Henry Dale, and A. V. Hill, these physiologists endeavoured to link governmental policy with research in university and industrial laboratories to create highly efficient joint research ventures that did not replicate work in any of the participating nations. The most famous result from these collaborations was penicillin, yet the questions I wish to pursue in this social history are broader than any story of scientific discovery. Did the transnational nature of physiological research exert an impact on the social, political, economic, and industrial structure of wartime science? And did Anglo-American physiologists play a significant role in the formation of government funded research and did their role stop there or did they serve broader diplomatic roles as well? In short, the answers to such questions, investigated in trans-Atlantic archives, may shed light on how these collaborations began and the way their existence promoted a longer-lasting influence on the organization of international science.