President George W Bush had nominated retired four-star Army Gen Peter Schoomaker to return to duty and become the army's new chief of staff.
In a highly unusual move, Defence Secretary Donald Rumsfeld last week recommended that Mr Bush ask the US Senate to approve Gen Schoomaker (57) who headed elite US Special Operations forces before retiring three years ago, to succeed. He succeeds Gen Eric Shinseki as the army's top officer.
Gen Shinseki retired last week and Mr Rumsfeld's choice of a retiree to vault past top active generals to head the service and become a member of the Joint Chiefs of Staff is expected to stir controversy in the Army and in Congress.
The nomination comes against a backdrop of strained relations between Mr Rumsfeld and the Army as the Defence secretary presses for major changes in the US military services to fight terrorism and wars in the 21st century.
Two other top Army generals, including Tommy Franks who was architect of the Iraq war plan, earlier turned down Mr Rumsfeld invitations to take the job.
Apart from Gen Douglas MacArthur who came out of retirement in 1941 to head allied forces in the Southwest Pacific in World War II, historians say they know of no previous case in which an officer was summoned out of retirement to serve as army chief of staff.
They said seven men had served as army senior officer or commanding general after earlier retiring from the military, but none since the Civil War.
One was George Washington, who served as senior officer of the Army in 1798 and 1799 after serving as the first US president.