JP 3-0, page 100

Chapter IV IV-8 JP 3-0 forces, including internal administration, personnel support, training, logistics, and Service intelligence operations. Further, functional and Service components of the joint force conduct supported, subordinate, and supporting operations, not independent campaigns. (1) Service Components. CCDRs and subordinate unified commanders conduct either single-Service or joint operations to accomplish a mission. All JFCs may conduct operations through their Service component commanders, lower-echelon Service force commanders, and/or functional component commanders. Conducting joint operations through Service components has certain advantages, which include clear and uncomplicated command lines. This arrangement is appropriate when stability, continuity, economy, ease of long-range planning, and scope of operations dictate organizational integrity of Service components. While sustainment remains a Service responsibility, there are exceptions such as arrangements described in Service support agreements, CCDR-directed common-user logistics lead Service, or DOD agency responsibilities. (2) Functional Components. The JFC can establish functional component commands to conduct operations when forces from two or more Services must operate in the same physical domain or accomplish a distinct aspect of the assigned mission. These conditions apply when the scope of operations requires that the similar capabilities and functions of forces from more than one Service be directed toward closely related objectives and unity of command is a primary consideration. For example, functionally oriented components are useful when the scope of operations is large and the JFC’s attention must be divided between major operations or phases of operations that are functionally dominated. Functional component commands are subordinate components of a joint force. Except for the JFSOCC/commander, joint special operations task force (JSOTF), functional components do not constitute a “joint force” with a JFC’s authorities and responsibilities, even when composed of forces from two or more Military Departments. (a) JFCs may conduct operations through functional components or employ them primarily to coordinate selected functions. The JFC will normally designate the Service component commander who has the preponderance of forces and the ability to command and control them as the functional component commander. However, the JFC will always consider the mission, nature and duration of the operation, force capabilities, and C2 capabilities when selecting a commander. The establishment of a functional component commander must not affect the command relationship between Service component commanders and the JFC. (b) The functional component commander’s staff composition should reflect the command’s composition so that the staff has the required expertise to help the commander effectively employ the component’s forces. Functional component staffs require advanced planning, appropriate training, and frequent exercises for efficient operations. Liaison elements from and to other components facilitate coordination and support. Staff billets and individuals to fill them should be identified and used when the commander forms the functional component staff for exercises and actual operations.