This monograph explores the subject of organizational learning with a particular emphasis on how military units learn in combat. The challenges of today's joint operating environment require groups of soldiers to adapt responsively to a wide array of difficult and sometimes unfamiliar tasks. These efforts to improve unit performance often occur in the middle of an operation and thus involve a quick adjustment of behavior under taxing circumstances. Some scholars promote the concept of "learning organizations" and suggest that, because of the special qualities they possess, such entities have the ability to learn and succeed in situations where others fall short. This is an attractive notion for leaders seeking transformation for their organizations, but it is not free from ambiguity. What accounts for episodes of failure in organizations that seem to learn regularly on other occasions? This study argues that the process of learning demands a deeper explanation, especially when it takes place in the complex environment of combat. Focused on a topic of chief importance to military leaders, this monograph examines organizational learning through a case study that considers one unit over the course of a six-month operation. In combat with the Japanese on the Philippine island of Luzon from February to July 1945, the soldiers of the 112th Cavalry Regiment faced a resourceful enemy whose resistance challenged them across a broad spectrum of conditions. How did the unit learn in these circumstances, and what factors facilitated the process? When elements of the regiment failed to learn, what accounted for that failure? Throughout the 112th's performance on Luzon, evidence of adaptation is not difficult to find. Harder to discern are the details behind how its officers and men arrived at those improvements. By mining a rich collection of primary sources - including daily unit journals, after action reports, diaries, memoirs, and interviews - this study sheds light on the p