10 U.S.C. § 12209

(a) Within such numbers as the Secretary concerned may prescribe, enlisted Reserves may, with their consent, be selected for training as officer candidates. Enlisted Reserves so selected shall be designated as officer candidates during that training. However, no member of the Army National Guard of the United States or the Air National Guard of the United States may be so selected or designated unless— (1) he is on active duty; or (2) the governor or other appropriate authority of the jurisdiction concerned consents. (b) The enlistment or term of service of a Reserve who is designated as an officer candidate under this section is extended to include any period, beyond its normal expiration date, during which he is an officer candidate. (c) While he is on active duty, other than active duty for training without pay, or performing authorized travel to and from that duty, an officer candidate designated under this section is entitled to the pay and allowances of his enlisted grade, but not less than those prescribed for pay grade E–2. (d) An officer candidate designated under this section may not participate in the program of a reserve officer training corps of any armed force.