James Schlesinger, who has died aged 85, was a hawkish and uncompromising Republican politician who served under three presidents. As US defence secretary between 1973 and 1975, he handled several international crises including the Yom Kippur War, the Turkish invasion of Cyprus, and the American evacuation of Vietnam in 1975, an event which he called a defeat of tragic proportions.
He was also Energy Secretary under President Jimmy Carter, a Democrat, and proved lukewarm on alternative energy and enthusiastic about nuclear power. Jane Fonda, the actress and anti-war activist, once joked that putting Mr Schlesinger in charge of nuclear power was like putting Dracula in charge of a bloodbank.
He was born in New York, the son of Jewish parents, and educated at the city's Horace Mann School and Harvard. For a time, he taught economics at the University of Virginia before joining the Richard Nixon administration in 1969.
He was appointed chairman of the Atomic Energy Commission before being promoted to director of the CIA, where he instituted significant change, making him deeply unpopular with staff. After six months, he was moved on and appointed Defence Secretary.
He was well-liked among military leaders, consulting with them frequently and aggressively lobbying Congress for more money for the armed forces. His pro-interventionist foreign policy also brought him favour with the new-right coalition of the day. He worked to rebuild military morale and revamp nuclear strategy in the turbulent period after the Vietnam War era. He opposed amnesty for draft resisters.
On nuclear weapons, he gained a reputation as a perceptive thinker on nuclear strategy, advocating a retreat from reliance on mutually assured destruction as a means of avoiding nuclear war with the Soviet Union. "Deterrence is not a substitute for defence," he said.
However, his bluntness and tenacity in military budget struggles made for often prickly relations with Congress and he clashed frequently with secretary of state Henry Kissinger. President Gerald Ford fired him in 1975 and replaced him with his White House chief of staff, Donald Rumsfeld.
But Mr Schlesinger was not gone for long. Two years later, he was back in the senior ranks of government, serving first as Mr Carter's energy tsar and then as the first secretary of the new Energy Department, created amid severe fuel shortages and soaring prices spawned by oil embargoes and tensions with Iran in the 1970s.
In 1979, he was sacked in a Cabinet shake-up and went on to work as a consultant and advisor to government on defence and energy.
In later years, he served on a host of defence and energy-related taskforces and advisory committees and continued to push for more sophisticated nuclear weapons systems. He was a long-time member of the Pentagon's Defence Policy Board and was appointed by President George W Bush to the Homeland Security Advisory Committee.
He was predeceased by his wife Rachel and survived by eight children.