The opportunity to retire evaded George Marshall. In September 1950, General Marshall, as he was called by everyone, left his office at the American Red Cross and was driven across the Potomac River to the Pentagon to be sworn into his new post as Secretary of Defense.If you did not know that the General of the Army George Marshall's last official office was Secretary of Defense, you would not be alone. For most people, his story ends with the Marshall Plan, and there has not been a biography dedicated to George Marshall in his final official role until now.