Japan's defeat of Russia in the Russo-Japanese War in 1905 sent shockwaves throughout the international community. Although largely overshadowed by other events during the 20th century, interest in the war has renewed over the past two decades. The geopolitical influence of the war, the subjective lens through which Western armies studied it, and its influence on Western military thought from 1905-1914 are three of the major themes of literature concerning the war. The purpose of this study is to determine the influence of the war on the U.S. Army from 1905-1914. This study analyzes how medical and engineers lessons from the war improved the U.S. Army's ability to conduct sustained offensive operations. This study uses observer reports from the war, records of institutional education during the early 20th century, and several professional military journals for its analysis. A short examination of medical and engineer operations in World War I, demonstrates how lessons from the war improved the ability of the U.S. Army to conduct sustained offensive operations.