The commander-in-chief of the US military at any given time is the president of the United States. This is established in the US Constitution, though in the past other high ranking military officials have also used the title “commander-in-chief” to refer to their position as commander of large operations. In 2002, however, it was declared that only the president of the US would use that title. The president is established as the commander-in-chief to create a central command structure in case of military action, with a chain of command running from the president to the secretary of defense and then to the combatant commanders.
In the US, the commander-in-chief of the US military is appointed by the Constitution. Article II of the US Constitution establishes the basic structure of the executive branch of the US government, and outlines some of the basic powers and responsibilities that the head of that branch has. Section 2 of Article II establishes presidential powers, and the first clause of that section indicates that the US President “shall be Commander in Chief of the Army and Navy of the United States.”
This enumeration of powers established the president as the commander-in-chief for the US, and this has been upheld since the drafting of the Constitution. The exact nature of the role of the president as the commander-in-chief can depend on the president and the approach he or she takes to this power. Some presidents, such as Abraham Lincoln and Lyndon Johnson, have rigidly controlled military actions during times of war, while other presidents have trusted military leaders to handle operations.
The title “commander-in-chief” has always been used by the US president, but other military commanders within the US military have often used the title as well. It was historically seen as an appropriate title for any high ranking commander that had other military officers within his or her command. In 2002, however, then Secretary of Defense Donald Rumsfeld announced the term would be used exclusively by the president. Other high ranking military officials would no longer be referred to as commanders-in-chiefs (CINCs), but the top commanders of various combatant commands would be referred to as combatant commanders.
A combatant commander is a top ranking military officer for a combatant command, with each command part of the Unified Combatant Command that makes up the top ranks of the US military. These various commands are typically charged with operations in a particular geographic region or a certain aspect of military operations such as special operations or transportation. The various combatant commanders are directly under the secretary of defense, who is the head of the Department of Defense and is appointed by and reports directly to the president.