How do communication patterns between diplomatic and military leadership change right before and during war? Do deliberation processes take place, and if so, when? Is it possible that European powers just inadvertently stumbled into World War I without any real discussion between diplomatic and military leadership? This so-called "Sleepwalkers"-hypothesis challenges narratives that emphasize deliberate decision-making, instead highlighting institutional inertia and breakdowns in cross-channel communication as key factors in the escalation to war. To test this, I collected and digitized the complete registers of the written communication sent from the German Foreign Ministry to the Kaiser and military leadership from 1910-1918, encompassing a total of over 21,000 register entries. This unique dataset allows a day-by-day examination of the volume, content and recipients of diplomatic communication regarding the war. The quantitative analyses reveal an unexpected pattern: a significant increase in communication occurred only days before the outbreak of hostilities, with little evidence of long-term coordination. This lack of cohesion suggests decision-makers operated in silos, relying on pre-existing plans and mutual misperceptions rather than cohesive policy. These results further qualify narratives of calculated aggression, highlighting systemic mismanagement and miscommunication as key factors in the path to war, and offering new insights into the dynamics of institutional decision-making and the conditions that can lead to conflict escalation.