Book excerpt: Doctrine provides a military organization with a common philosophy, a language, a purpose, and unity of effort. Tactics is the art and science of employing all available means to win battles and engagements. Specifically, it comprises the actions taken by a commander to arrange units and activities in relation to each other and the enemy. FM 3-90 introduces the basic concepts and control measures associated with the art of tactics. It cannot be read in isolation. To understand FM 3-90, the reader must understand the operational art, principles of war, and links between the operational and tactical levels of war described in FM 3-0, Operations. He should understand how the activities described in FM 3-07, Stability Operations and Support Operations, carry over and affect offensive and defensive operations and vice versa. He should understand the operations (plan, prepare, execute, and assess) process described in FM 6-0, Command and Control, and how that process relates to the military decision making process and troop-leading procedures described in FM 5-0, Army Planning and Orders Production. FM 3-90 also refers to joint publications (JPs). Reviewing referenced JPs will also aid in understanding FM 3-90. FM 3-90 focuses on the tactics used to employ available means to win in combat. Those tactics require judgment in application. The ability to seize and secure terrain, with its populations and productive capacity, distinguishes land forces conducting decisive offensive and defensive operations. FM 3-90 provides a common discussion of how commanders from the battalion task force level through the corps echelon conduct tactical offensive and defensive operations and their supporting tactical enabling operations. It is not prescriptive, but authoritative. Tactical fundamentals do not change with the fielding of each new piece of equipment. However, the integration of new equipment and organizations usually requires changes in related techniques and procedures. FM 3-90 provides guidance in the form of combat-tested concepts and ideas modified to exploit emerging Army and joint capabilities.