This research details a point of reference to understand two case studies of cooperation that developed among lower-level, or non policy-making bureaucrats during times of conflict or war. Using components of game theory, I propose that when an international conflictual relationship occurs that resembles an iterated Prisoners' Dilemma, and that meets certain conditions, tacit cooperation can emerge. Tacit cooperation consists of illicit or implied cooperation that is not sanctioned at the national policy level.In this research I develop a framework of tacit cooperation, relying heavily upon Robert Axelrod's theory of evolutionary cooperation. With the framework in place, I then explicate two international case studies, World War I trench warfare cooperation and the INF "walk in the woods" between Kvitsinsky and Nitze, to show how the theory can be used to describe ways that cooperation can occur in a hostile or conflictual environment.