HE RARELY speaks in public and almost never to the press. Most of his reports are secret. A historian once asked if even his brain was classified. But for over four decades Andrew Marshall’s judgments, emanating from a small office in the Pentagon, have guided American defence policy. Or so, at least, his supporters say.

Mr Marshall, now 93, headed the Office of Net Assessment (ONA), known as the Pentagon’s internal think-tank, from its creation in 1973 to his retirement on January 2nd. Such was his longevity and wisdom that some defence cognoscenti took to calling him “Yoda”, after the character from “Star Wars”. The nickname is also a reference to his tutoring of influential scholars and officials. This coterie of experts, who refer to themselves as alumni of “St Andrew’s Prep”, speak of their inscrutable teacher with awe.

In a new book on Mr Marshall two of his acolytes, Andrew Krepinevich and Barry Watts, compare him to such foreign-policy luminaries as Henry Kissinger and James Schlesinger. Tasked with considering emerging trends and long-term strategy, the ONA has been credited with foreseeing the demise of the Soviet Union and the rise of China. But Mr Marshall is perhaps most noted for his belief that warfare is subject to dramatic change when new technologies combine with doctrinal and operational innovation to create a “revolution in military affairs” (RMA). In the 1980s he predicted a new RMA driven by technologies such as advanced sensors, precision-guided weapons and computer networks.

Most Americans have never heard of Mr Marshall, but his ideas have drawn attention far beyond America’s shores. Chinese and Russian military strategists pore over his work, which often portrays their countries as significant threats. In an interview with The Economist in 2012, General Chen Zhou, who has written several of China’s defence white papers, said: “We studied RMA exhaustively. Our great hero was Andy Marshall in the Pentagon. We translated every word he wrote.”

Much of this admiration seems genuine, but money may also play a role. “Chen knows that Marshall is good for his budgets,” says Jonathan Pollack of the Brookings Institution, a think-tank. The same could be said of Mr Marshall’s American devotees. The ONA relies on a small network of outside contractors and individuals, often alumni of St Andy’s, to provide analysis. One large recipient of its cash is the Centre for Strategic and Budgetary Assessments, a think-tank that is led by Mr Krepinevich and once employed Mr Watts.

The less starry-eyed claim that Mr Marshall hedged his predictions and exaggerated threats. He may have outdone the CIA in noting the burden of military spending on the Soviet economy, but he also saw the doomed state as an enduring menace. His dark view of China strikes some as alarmist. And his thoughts are not always original—the RMA, for example, was a Soviet concept. As a result, his influence is probably overstated: only one of the 12 defence secretaries under whom he served makes more than a perfunctory reference to him in his memoirs, notes Michael Desch, a professor at the University of Notre Dame.

The problem with the hagiographic treatment of Mr Marshall, say those outside his circle, is that it is hard to check the often classified facts. “We have an incomplete picture of him because only genuine intimates speak on his behalf,” says Mr Pollack. He and others would like to see more scrutiny of the ONA. “The time is long past for a serious assessment of what the office has contributed,” says Mr Desch.

That view has grown within the Pentagon. In 2013, as defence officials faced sequester cuts, there was talk of closing the ONA, despite its tiny budget ($19m) and little more than a dozen staff. Instead, its direct line to the secretary of defence was cut and it now reports to a lower-ranking official. Nevertheless, the search is on for a new futurist-in-chief. Finding another Andrew Marshall will not be easy, laments Mr Watts. Perhaps easier, though, than predicting where the world will go next.