During World War One, approximately 4,000 French rank soldiers and NCOs were detached to serve as military interpreters alongside the British and later American troops. These men from all walks of life whose one point in common was the command of the English language, very quickly became the crucial lynchpins of Allied coalition practical functioning. They contributed to the ultimate military victory through two essential tasks: establishing vital communications between the British and American military and the local civilians and authorities, but also assuming crucial liaison duties on the battle field between the different armies. This particularly well-documented group of individuals not only provides a unique insight into the functioning of the Allied coalition, but also raises fascinating questions about the construction of identity in time of war. Over the course of our graduate work we have been able to assemble both quantitative data (database with detailed information on 2700 individuals constructed from military records, including their social and geographic origins and professional experience before the war) and qualitative data (great number of published and un-published memoirs, as well as other writing) and are thus in a good position to establish hypotheses about the particular role these men occupied and the impact it had on them. For the duration of the war, they remained French soldiers, yet they lived with British officers, socializing with them in the officers’ mess, subjected to their incessant requests to explain particular French traditions. Their uniform was curiously hybrid: British khaki, but with special “Interpreter” buttons and a French headdress, the kepi. In the villages behind the frontlines, they settled negotiations between the British military, to whom they felt affinity because of the shared military effort to which they were contributing, and the French civilian population, their own countrymen. Spending the war far from where the French army was defending their own fatherland, and furthermore in non-combatant roles, made the interpreters very vocal about the various tensions they were under. This subject falls in the category of objects that require new and innovative methodological approaches, as comparison and even transfer studies fail to grasp what these men accomplish between two very different military cultures and institutions. While “histoire croisée” has provided a useful entry point, it is really Translation Studies and Interpreting Studies which enable a full understanding. It is hoped that this paper would contribute to a larger reflection on the role of both language and loyalty to an institution and a social group for individuals bridging language and cultural borders during military conflict.