Field Manual (FM) 3-34.400, "General Engineering," is the primary implementing manual for the engineer function that bears its name (the others being combat and geospatial engineering). This manual provides general engineering (GE) doctrine for the United States (U.S.) Army and U.S. Marine Corps. 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.