Before becoming Army secretary, Mr. Hoffmann was a soldier, a congressional aide and a close adviser to James R. Schlesinger when Mr. Schlesinger headed the Atomic Energy Commission and the Defense Department — so close that The New York Times referred to him as Mr. Schlesinger’s “alter ego and troubleshooter.” President Gerald R. Ford appointed Mr. Hoffmann Army secretary in 1975 to succeed Howard H. Callaway, who had resigned to manage Ford’s 1976 presidential campaign. Mr. Hoffmann oversaw the transition to an all-volunteer Army in June 1973 as the Vietnam War wound down. He devoted particular attention to making sure that blacks were not concentrated in combat roles as Army studies indicated they had been. The number of black noncommissioned officers rose under his leadership, while racial incidents declined at home and overseas. He moved to Colorado Springs as a child, then went back east to attend Princeton, graduating in 1954. Facing the draft, he enlisted in the Army and became aide-de-camp to the commanding general of the 101st Airborne Division. He left active service as a first lieutenant but stayed in the Army Reserve and rose there to the rank of major. He resigned in 1975 when he became the service’s civilian chief. Mr. Hoffmann graduated from the University of Virginia School of Law in 1961, then became a clerk for Judge Albert V. Bryan on the United States Court of Appeals for the Fourth Circuit in Virginia. He worked next as an assistant United States attorney in Washington, then was minority counsel for the House Judiciary Committee and legal counsel to Senator Charles H. Percy, Republican of Illinois, before becoming an aide to Mr. Schlesinger. His rise was also aided by his close friendship with Donald H. Rumsfeld, a fellow member of the Cap and Gown Club at Princeton who was President Ford’s chief of staff and Mr. Schlesinger’s successor as defense secretary. When Mr. Rumsfeld returned as defense secretary under President George W. Bush, Mr. Hoffmann advised him on the war in Afghanistan and on traumatic brain injuries suffered in combat. Mr. Hoffmann is survived by his wife of 52 years, the former Margaret McCabe, who is known as Muggy; his daughter, Cecil Hoffmann Slye; his sons, William and Bernhard; his sisters, Elizabeth Longstreet, Cecil Hoffmann and Molly MacKinnon; and three grandchildren.