All commissioned officers in the U.S. military take the Oath of Office when they commission as officers in their respective branch of service.

Commissioned Officer Oath Of Office. It is traditional for officers to recite the oath upon promotion but as long as the officer's service is continuous this is not required. “I, (state your name), having been appointed a (rank) in the United States (branch of service), do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foriegn and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation … It differs from that of the oath of enlistment that enlisted members recite when they enter the service. All officers of the eight uniformed services of the United States swear or affirm an oath of office upon commissioning. It is required by statute, the oath being prescribed by Section 3331, Title 5, United States Code.