According to many historians, the Russo-Japanese War 1904ー1905 was considered to be the first war fought between two equal industrialized powers. The war attracted much attention from the major powers in the world due in part to the use of many new military innovations and technologies, especially on the tactical level. In Sweden, lessons observed from the naval war came to heavily influence the debate regarding the armament of the Swedish Naval Defence. However, barely any previous research has sought to analyze what tactical lessons the Swedish Army learned from the war. The purpose of this study is therefore to analyze what tactical lessons Sweden learned from the Russo-Japanese War 1904ー1905. The research questions presented in this study are: What lessons did the Swedish Army identify from the war relating to the three main arms of the Army: the infantry, the artillery and the cavalry? Which pitfalls occurred during the learning process? To what extent were the lessons implemented? The theoretical framework for this essay is based on Brent Sterling’s theory regarding recurring pitfalls when learning from foreign wars. To identify the lessons learned from the Russo-Japanese War, articles published in the journal of The Royal Swedish Academy of War Sciences during and after the war have been analyzed, as well as a compendium published by the Swedish General Staff. The methodology used to analyze the source material is a qualitative text analysis with a hermeneutical approach. The results from the study show that many different lessons from the war relating to the three arms were identified. Among these were the impressive effectiveness of the machine gun, the devastating indirect fire wrought by howitzers and the importance of correctly utilizing the cavalry. However, multiple pitfalls also occurred during the learning process relating to the all three arms as well. Lessons learned from the war also paved the way for the implementation of the machine gun and the howitzer in the Swedish Army.