4-73. In all joint operations, sustainment is a Service responsibility except as specified by DOD combatant command support agent directives, combatant commanders’ lead Service designations, or inter-Service support agreements. Combatant commanders direct theater army commanders to provide common-user logistics and ASOS, agencies, or multinational forces, as required. However, shared sustainment responsibility or common-user logistics is more effective, especially for joint operations. Directive authority for logistics is the additional authority used by combatant commanders to eliminate duplicated or overlapped sustainment responsibilities. The theater army coordinates with the combatant command staff to determine joint sustainment requirements, identify responsibilities, and enable commanders to exercise mission command for sustainment. (See ADRP 4-0 for more information on sustainment.)