US Code
CHAPTER 715— APPOINTMENTS IN THE REGULAR ARMY
§ 7153. Commissioned officers: appointment without specification of branch; transfer between branches

(a) Appointments in commissioned grades in the Regular Army shall be made without specification of branch except in each of the special branches and as professors or director of admissions of the United States Military Academy.
(b) Commissioned officers appointed in the Regular Army without specification of branch shall be assigned, and may be transferred and reassigned, by the Secretary of the Army to branches other than the special branches, according to their professional qualifications and the needs of the Army.