According to U.S. Army Doctrine, a theater army headquarters is the army service component command assigned to a geographic combatant command. It is organized, manned and equipped to perform 3 roles:
A theater army is responsible for the administration and support of all United States Army forces assigned, attached, under the operational control of a geographic combatant command or transitioning to that area of responsibility (AOR). For example, United States Army Central (Formerly the Third United States Army) which is a theater army is responsible for the administration and support of all U.S. Army forces assigned, attached, under the operational control of United States Central Command, or transitioning into its area of responsibility. The theater army also provides most of the administrative control and army support to forces deployed in the joint operations area. In addition to these functions the theater army has a significant role in: coordinating, supporting, integrating all formations above brigade forces into geographic combatant command plans for that area of responsibility, and providing common-user logistics and Army executive agent services for all Army and joint forces operating in that AOR. The theater army is also responsible for distribution, recovery, and redistribution of supplies and equipment in joint operations areas. 5 The theater army enables the combatant commander to employ across the scope of military operations.
Each theater army supports the Army strategic roles—prevent, shape, and win—and facilitates the use of landpower in JTFs
Theater Armies exercise operational control of all army forces under its command until the combatant commander attaches units to a subordinate joint command. The theater army retains administrative control of all army forces in the command regardless of whether the theater army has operational control over them; this responsibility extends to the entirety of the U.S. Army.
The theater army commander remains responsible to the Department of the Army for Service-specific requirements. This falls under the ADCON chain of authority
Responsibilities of a Service component are determined from Title 10; DODD 5101.1; DA Memo 1-10; and combatant commander’s daily operational requirements.
These responsibilities may include:
Additionally, the theater army is also responsible for administrative control of all U.S. Army forces in that AOR during times of peace and war.
FM 3-94 THEATER ARMY, CORPS, AND DIVISION OPERATIONS. Washington, DC: Department of the Army. 2014. ↩
Dr. Christopher R. Paparone Army Logistician COCOM, ADCON, OPCON, TACON Support —Do You Know the Difference? http://www.alu.army.mil/alog/issues/novdec07/cmmd_relat_difference.html ↩
ATP 3-93 - Theater Army Operations. United States Army. 2014. pp. 1–1, 1–2, 1–3, 1–4, 1–5. ↩
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U.S. Army Public Affairs (21 August 2020) Army announces its service component command for U.S. Space Command https://www.army.mil/article/238376/army_announces_its_service_component_command_for_u_s_space_command ↩