In the literature on the struggles of African Americans during the First World War, there has been a failure to examine the experiences of the 325(th )Field Signal Battalion, the first Black signal unit in the U.S. Army. Drawing upon a range of archival sources, unpublished letters, official documents and newspapers, this article assesses the experiences of the battalion's Black officers and men before, during and after the war, arguing that they defied not only traditional notions of specialism within the army, threatening to destabilize unambiguous racial boundaries by challenging what had long been viewed as an intrinsically white soldiers' sphere of influence, but also some of the fundamental principles underpinning Jim Crow ideology. In so doing, they made an important, albeit subtle, contribution to the 'long civil rights movement'.