10 U.S.C. § 7324: Forty years or more: Army officers

(a) Except as provided in section 1186 of this title, a commissioned officer of the Army who has at least 40 years of service computed under section 7326 of this title shall be retired upon his request. (b) Any warrant officer of the Army who has at least 40 years of service computed under section 7326(a) of this title shall be retired upon his request.