Army Techniques Publication ATP 1-20 discusses field history operations and provides guidance on the organization and employment of Army historians. It details the techniques and procedures for the documentation, recording, and preservation of the official history of the Army during combat and contingency operations. The principal audiences for ATP 1-20 are Army commanders, staffs, leaders, and those Soldiers and civilians assigned to historical duties. It outlines responsibilities for commanders and units and the necessary doctrinal guidance for unit historical officers (UHO), military history detachments (MHD), and other field historians to perform historical tasks across the range of military operations. ATP 1-20 helps commanders, and Army field historians assigned to them, with their responsibilities to ensure that Army operational history is captured and preserved, with particular attention to command and unit history officers and MHDs. It is applicable at all command levels of the operational Army that may deploy and perform combat and contingency operations. The doctrinal principles and procedures in this publication provide guidance and are not prescriptive. However, they reflect hard lessons learned over the course of Army history, especially when its operational history was not adequately captured or preserved. ATP 1-20 applies to the Active Army, Army National Guard/Army National Guard of the United States, and United States Army Reserve unless otherwise stated.