In the closing debate of the 2008 Péronne conference Jay Winter criticised the extent to which First World War has remained locked into national frames of reference. He called for future research to take up the transnational challenge. I would like to add a modest contribution, not by choosing a strictly comparative method, but rather by sketching what the concept of “croisée“ can contribute to the historiography of Allied warfare during World War One. In order to do this, I will use an “objet à croisement instrinsèque” which gives me access to this history which is so thoroughly anchored between two national frameworks that a comparative approach does not do it justice: the role played by military interpreters on the Western Front. The history of Allied warfare tends to be written top-down, in the British case especially by focussing almost exclusively on the role of high command. This paper therefore takes on Allied cooperation from the opposite end of the spectrum by examining contact and interaction between British soldiers and French civilians, as observed and facilitated by the French military interpreters attached to British units. By looking at the modalities and limits of linguistic exchange, as portrayed in memoirs penned by interpreters and the British officers they frequented, and the more largely at the power politics, responsibilities and tensions which emerge from the official reports kept as part of the archives of the Mission Militaire Francaise auprès de l’Armée Britannique, I intend to show the extent to which allied warfare even on a micro-level was never straightforward and how a complicated system was necessary to maintain the balance which in the end led to Allied success.