Source is DA Memo 600-8-22, dtd 9 July 2001, linked:
http://www.army.mil/usapa/epubs/pdf/m600_8_22.pdf
Approval Authority has been delegated to a mixed bag of positions. They include the Administrative Assistant to the Secretary of the Army, Assistant Secretaries of the Army (SES-4 or above), agencies headed by a LTG/MG, the Chief of Staff and Vice Chief of Staff of the US Army...
In the beginning it was the President, and that was delegated to the War Department in 1943. President Eisenhower revised that by Executive Order in '55.
Thank you Jinxie!! *HUGS!*