Unified combatant command

In the European Theater, Allied military forces fell under the command of the Supreme Headquarters Allied Expeditionary Force (SHAEF). After SHAEF was dissolved at the end of the war, the American forces were unified under a single command, the US Forces, European Theater (USFET), commanded by General of the Army Dwight D. Eisenhower. A truly unified command for the Pacific War proved more difficult to organize, as neither General of the Army Douglas MacArthur nor Fleet Admiral Chester W. Nimitz was willing to be subordinate to the other, for reasons of interservice rivalry.[15]

The Joint Chiefs of Staff continued to advocate in favor of establishing permanent unified commands, and President Harry S. Truman approved the first plan on 14 December 1946.[16] Known as the "Outline Command Plan", it would become the first in a series of Unified Command Plans. The original "Outline Command Plan" of 1946 established seven unified commands: Far East Command, Pacific Command, Alaskan Command, Northeast Command, the U.S. Atlantic Fleet, Caribbean Command, and European Command. However, on 5 August 1947, the CNO recommended instead that CINCLANTFLT be established as a fully unified commander under the broader title of Commander in Chief, Atlantic (CINCLANT). The Army and Air Force objected, and CINCLANTFLT was activated as a unified command on 1 November 1947. A few days later, the CNO renewed his suggestion for the establishment of a unified Atlantic Command. This time his colleagues withdrew their objections, and on 1 December 1947, the U.S. Atlantic Command (LANTCOM) was created under the Commander in Chief, Atlantic (CINCLANT).[17]

Under the original plan, each of the unified commands operated with one of the service chiefs (the Chief of Staff of the Army or Air Force, or the Chief of Naval Operations) serving as an executive agent representing the Joint Chiefs of Staff.[18] This arrangement was formalized on 21 April 1948 as part of a policy paper titled the "Function of the Armed Forces and the Joint Chiefs of Staff" (informally known as the "Key West Agreement").[19] The responsibilities of the unified commands were further expanded on 7 September 1948 when the commanders' authority was extended to include the coordination of the administrative and logistical functions in addition to their combat responsibilities.[20]

Far East Command and U.S. Northeast Command were disestablished under the Unified Command Plan of 1956–1957.

A 1958 "reorganization in National Command Authority relations with the joint commands" with a "direct channel" to unified commands such as Continental Air Defense Command (CONAD) was effected after President Dwight Eisenhower expressed concern about nuclear command and control.[21] CONAD itself was disestablished in 1975.

Although not part of the original plan, the Joint Chiefs of Staff also created specified commands that had broad and continuing missions but were composed of forces from only one service.[22] Examples include the U.S. Naval Forces, Eastern Atlantic and Mediterranean and the U.S. Air Force's Strategic Air Command. Like the unified commands, the specified commands reported directly to the JCS instead of their respective service chiefs.[23] These commands have not existed since the Strategic Air Command was disestablished in 1992. The relevant section of federal law, however, remains unchanged, and the President retains the power to establish a new specified command.[24]

The Goldwater–Nichols Defense Reorganization Act of 1986 clarified and codified responsibilities that commanders-in-chief (CINCs) undertook, and which were first given legal status in 1947. After that act,[25] CINCs reported directly to the United States Secretary of Defense, and through him to the President of the United States.

The U.S. Atlantic Command became the Joint Forces Command in the 1990s after the Soviet threat to the North Atlantic had disappeared and the need rose for an integrating and experimentation command for forces in the continental United States. Joint Forces Command was disbanded on 3 August 2011 and its components placed under the Joint Staff and other combatant commands.

On 24 October 2002, Secretary of Defense Donald H. Rumsfeld announced that in accordance with Title 10 of the US Code (USC), the title of "Commander-in-Chief" would thereafter be reserved for the President, consistent with the terms of Article II of the United States Constitution. Thereafter, the military CINCs would be known as "combatant commanders", as heads of the unified combatant commands.[26]

A sixth geographical unified command, United States Africa Command (USAFRICOM), was approved and established in 2007 for Africa. It operated under U.S. European Command as a sub-unified command during its first year, and transitioned to independent Unified Command Status in October 2008. In 2009, it focused on synchronizing hundreds of activities inherited from three regional commands that previously coordinated U.S. military relations in Africa.[27]

President Donald Trump announced on 18 August 2017 that the United States Cyber Command (USCYBERCOM) would be elevated to the status of a unified combatant command from a sub-unified command. It was also announced that the separation of the command from the NSA would be considered.[28][29] USCYBERCOM was elevated on 4 May 2018.

Vice President Mike Pence announced on 18 December 2018 that President Donald Trump had issued a memorandum ordering the stand-up of a United States Space Command (USSPACECOM).[30] A previous unified combantant command for unified space operations was decommissioned in 2002. The new USSPACECOM will include "(1) all the general responsibilities of a Unified Combatant Command; (2) the space-related responsibilities previously assigned to the Commander, United States Strategic Command; and (3) the responsibilities of Joint Force Provider and Joint Force Trainer for Space Operations Forces".[31] USSPACECOM was re-established on 29 August 2019.

A sub-unified command, or, subordinate unified command, may be established by combatant commanders when authorized to do so by the Secretary of Defense or the president.[34] They are created to conduct a portion of the mission or tasking of their parent geographic or functional command. Sub-unified commands may be either functional or geographic, and the commanders of sub-unified commands exercise authority similar to that of combatant commanders.

Examples of current and former sub-unified commands are the Alaskan Command (ALCOM) under USNORTHCOM, the United States Forces Korea (USFK) under USINDOPACOM, and United States Forces—Afghanistan (USFOR-A) under USCENTCOM.