It has been said that the only thing new in the world is the history you don't know. This Global War on Terrorism (GWOT) Occasional Paper (OP) is a timely reminder for the US Army about the history we do not know, or at least the history we do not know well. The Army has recently embarked on massive advisory missions with foreign militaries in Iraq, Afghanistan, and elsewhere around the globe. We are simultaneously engaged in a huge effort to learn how to conduct those missions for which we do no consistently prepare. Mr. Robert Ramsey's historical study examines three cases in which the US Army has performed this same mission in the last half of the 20th century. In Korea during the 1950s, in Vietnam in the 1960s and 1970s, and in El Salvador in the 1980s the Army was tasked to build and advise host nation armies during a time of war. The author makes several key arguments about the lesson the Army though it learned at the time. Among the key points Mr. Ramsey makes are the need for US advisors to have extensive language and cultural training, the lesser importance for them of technical and tactical skills training, and the need to adapt US organizational concepts, training techniques, and tactics to local conditions. Accordingly, he also notes the great importance of the host nation's leadership buying into and actively supporting the development of a performance-based selection, training, and promotion system. To its credit, the institutional Army learned these hard lessons, form successes and failures, during and after each of the cases examined in this study. However, they were often forgotten as the Army prepared for the next major conventional conflict. These lessons are still important and relevant today. In fact, prior to its publication the conclusions of this study were delivered by the author to several of the Army's current advisory training task forces. We at CSI believe this GWOT OP can contribute significant insights to the Army as it works to prepare for and conduct its current advisory missions.