During the French Revolutionary and Napoleonic Wars, British doctors travelled in unprecedented numbers to foreign locations where they were confronted with battlefield injuries, virulent and mysterious diseases, and complex military politics that few had encountered before. Drawing on rare manuscript sources, Kelly examines how nearly twenty-five years of sustained warfare affected the professional identity embraced by those doctors and thoroughly militarized their approach to medicine. This study demonstrates the emergence of the 'military medical officer' and places their work within the broader context of changes to British medicine during the first half of the nineteenth century.