Now, the arms race is threatening to revive, though in a new form.
The United States has an active hypersonic program of its own, as do Russia and, among others, North Korea. But the U.S. program has run into its own technical difficulties, including a booster failure last week.
Both China and the United States have the resources to work out the bugs, and the concern of many arms control experts is that it could become a new form of competition — at the very moment that President Biden has been looking for ways to avoid a proposed trillion-dollar modernization of the American nuclear forces and delivery systems.
The fact that the Pentagon was so surprised may explain why it stayed silent after the revelation of the test. John Kirby, the Pentagon spokesman, declined to confirm the test after the first report, in the Financial Times, and even after General Milley spoke, the Pentagon would say nothing about it.
What apparently made the Chinese test unsettling was that — in a first — it combined two well-known military technologies that previously had been developed separately, starting a half-century ago.
The first part of the prototype weapon circled the globe before speeding toward its target — paralleling a nuclear approach that the Soviet Union had pioneered in 1960s. Known as the Fractional Orbital Bombardment System, or FOBS, the Soviet concept was to send a warhead into a partial orbit of the Earth before it plunged back through the atmosphere toward a target.
The system was seen as ideal for surprise attacks because the weapon could fly on any course — even over the South Pole — and in theory could evade radars and detection. However, the United States quickly lofted early-warning satellites that could spot the bright flames of rising Soviet missiles and diminish the element of surprise.
Separately, the Soviets and others worked to develop hypersonic weapons, which could fly at more than five times the speed of sound, sometimes to deliver conventional weapons, not nuclear warheads.