Field Manual (FM) 3-34.400 is the primary implementing manual for the engineer function that bears its name (the others being combat and geospatial engineering). This FM provides the linkage between the engineering doctrine contained in FM 3-0, FM 3-34, and Joint Publication (JP) 3-34. It specifically draws from the material presented in the Army's keystone engineer manual (FM 3-34) and should always be used with an understanding of its relationship to that manual and its role as the keystone engineer manual. As the implementing manual for the engineer function of general engineering (GE), FM 3-34.400 describes the operational environment (OE) and how to apply and integrate GE principles in support of full spectrum operations and the linkage of GE to assured mobility. This FM focuses on the establishment and maintenance of lines of communications (LOCs) and sustainment operations that support operational requirements throughout the area of operations (AO). FM 3-34.400 is designed primarily to assist Army engineers at all echelons in planning and coordinating GE operations at the strategic, operational, and tactical levels. It is also a resource applicable to Department of Defense (DOD), joint, and other Army organizations and agencies that have a role in supporting, establishing, and/or maintaining the infrastructure required to conduct and sustain military operations. It is the primary manual to define the engineer function of GE. FM 3-34.400 is applicable across full spectrum operations. This includes the four types of Army operations (offense, defense, stability, and/or civil support) across the spectrum of conflict (peace, crisis, and war). This FM recognizes the need for joint interdependence and the reality that operations will frequently be performed in a joint, interagency, and multinational environment. This FM describes in detail how to apply the principles of GE when planning and executing GE functions, and is broken down into the following three major parts: Part One defines GE in the OE. It provides the staff engineer with the basic concepts and principals necessary to be successful in planning GE missions in support of joint, interagency, and multinational operations. Part Two defines the roles and functions associated with gaining and maintaining LOC in support of mobility. It details the responsibilities, planning, and construction/repair actions necessary to assist the force commander in deploying, maneuvering, and redeploying the force. Part Three provides information on missions that empower engineers to support sustainment of the force. It includes discussions on procurement of materials, protection support, facilities of various types, base camps, power generation and distribution, well-drilling, and real estate operations. Although it may be helpful for units conducting construction projects on post, it is not intended to specifically address or focus on the myriad of challenges associated with normal base operations in the continental United States (CONUS) or permanent overseas locations.