32 U.S.C. § 310

(a) (1) Notwithstanding sections 307 and 309 of this title, if a second lieutenant of the National Guard is promoted to the grade of first lieutenant to fill a vacancy in a federally recognized unit in the National Guard, Federal recognition is automatically extended to that officer in the grade of first lieutenant, effective as of the date on which that officer has completed the service in the grade specified in section 14303(a)(1) of title 10 and has met such other requirements as prescribed by the Secretary concerned under section 14308(b) of that title, if the officer has remained in an active status since the officer was so recommended. (2) Notwithstanding sections 307 and 309 of this title, if a warrant officer, W–1, of the National Guard is promoted to the grade of chief warrant officer, W–2, to fill a vacancy in a federally recognized unit in the National Guard, Federal recognition is automatically extended to that officer in the grade of chief warrant officer, W–2, effective as of the date on which that officer has completed the service in the grade prescribed by the Secretary concerned under section 12242 of title 10 , if the warrant officer has remained in an active status since the warrant officer was so recommended. (b) Notwithstanding sections 307 and 309 of this title, if an officer of the Army Reserve or the Air Force Reserve in a reserve grade above second lieutenant is appointed in the next higher grade in the National Guard to fill a vacancy in a federally recognized unit in the National Guard, Federal recognition is automatically extended to that officer in the grade in which the officer is so appointed in the National Guard if the officer has been recommended for promotion under chapter 1405 of title 10 and has remained in an active status since the officer was so recommended. The extension of Federal recognition under this subsection is effective as of the date when the officer is appointed in the National Guard.