The hallmark of the twentieth-century battlefield was the increasingly effective practice of "combined arms" warfare-the combining of various "combat arms" (infantry, cavalry, armor, artillery) to accomplish the mission. In the vanguard of this development was the use of artillery to support the mission of infantry on the battlefield. Although artillery bombardment was responsible for most deaths on the battlefield, armies rarely paired infantry and artillery in the assault. Between the two world wars the U.S. Army concluded that field artillery had an important role to play in its evolving combined arms doctrine. The new doctrine emphasized mobile, mechanized warfare and the crucial importance of artillery firepower in support of infantry. The most satisfactory arrangement for providing close artillery support was to locate artillery observers in the air over the battlefield and on the ground to accompany maneuvering infantry. The pairing of American infantry and artillery reached fruition in the European and Pacific Theaters of the Second World War. What is missing from the historical literature on combined arms, however, is the study of how that togetherness evolved. This dissertation will argue that the establishment of forward observer teams at the battle's front line that provided the vital link between infantrymen and the artillery batteries supporting them. To assess these developments in the union of combined arms theory and practice, this dissertation will be organized in three parts. The first will trace the inception of indirect fire and the evolution of field artillery tactical doctrine through 1941. The second section, which will be the heart of the study, will follow the experiences of forward observer personnel from tow U.S. Army Divisions in the Second World War. The 87th Infantry Division in Europe and the 37th Infantry Division [Ohio National Guard] in the Pacific will be examined as case studies. By studying one division from both theaters of the.