All officers of the seven uniformed services of the United States swear or affirm an oath of office upon commissioning. It differs slightly from that of the oath of enlistment that enlisted members recite when they enter the service. It is required by statute, the oath being prescribed by Section 3331, Title 5, United States Code. 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.
Text of the Oath
The oath is for an indeterminate period; no duration is specifically defined.
Officers of the National Guard of the various States, however, take an additional oath:
Commissioned officers (O-1 (second lieutenant or ensign) through O-10 (general or admiral) and W-2 through W-5 (chief warrant officers)) are commissioned under the authority of the President of the United States with the advice and consent of the United States Senate; warrant officers (W-1) receive a warrant under the authority of their respective service secretary (e.g., the Secretary of the Army or the Secretary of the Navy); National Guard officers are additionally committed to the authority of the governor of their state. They may be activated in the service of their state in time of local or state emergency in addition to federal activation. Reserve officers may only be activated by the President of the United States.