The enthusiasm has spread to military contractors, especially after the Pentagon awarded the largest one, Lockheed Martin, more than $1.4 billion in 2018 to build missile prototypes that can be launched by Air Force fighter jets and B-52 bombers. These programs were just the beginning of what the acting defense secretary, Patrick M. Shanahan, described in December as the Trump administration’s goal of “industrializing” hypersonic missile production. Several months later, he and Griffin created a new Space Development Agency of some 225 people, tasked with putting a network of sensors in low-earth orbit that would track incoming hypersonic missiles and direct American hypersonic attacks. This isn’t the network’s only purpose, but it will have “a war-fighting capability, should it come to that,” Griffin said in March.

Development of hypersonics is moving so quickly, however, that it threatens to outpace any real discussion about the potential perils of such weapons, including how they may disrupt efforts to avoid accidental conflict, especially during crises. There are currently no international agreements on how or when hypersonic missiles can be used, nor are there any plans between any countries to start those discussions. Instead, the rush to possess weapons of incredible speed and maneuverability has pushed the United States into a new arms race with Russia and China — one that could, some experts worry, upend existing norms of deterrence and renew Cold War-era tensions.

Although hypersonic missiles can in theory carry nuclear warheads, those being developed by the United States will only be equipped with small conventional explosives. With a length between just five and 10 feet, weighing about 500 pounds and encased in materials like ceramic and carbon fiber composites or nickel-chromium superalloys, the missiles function like nearly invisible power drills that smash holes in their targets, to catastrophic effect. After their launch — whether from the ground, from airplanes or from submarines — they are pulled by gravity as they descend from a powered ascent, or propelled by highly advanced engines. The missiles’ kinetic energy at the time of impact, at speeds of at least 1,150 miles per hour, makes them powerful enough to penetrate any building material or armored plating with the force of three to four tons of TNT.

They could be aimed, in theory, at Russian nuclear-armed ballistic missiles being carried on trucks or rails. Or the Chinese could use their own versions of these missiles to target American bombers and other aircraft at bases in Japan or Guam. Or the missiles could attack vital land- or sea-based radars anywhere, or military headquarters in Asian ports or near European cities. The weapons could even suddenly pierce the steel decks of one of America’s 11 multibillion-dollar aircraft carriers, instantly stopping flight operations, a vulnerability that might eventually render the floating behemoths obsolete. Hypersonic missiles are also ideal for waging a decapitation strike — assassinating a country’s top military or political officials. “Instant leader-killers,” a former Obama administration White House official, who asked not to be named, said in an interview.

Within the next decade, these new weapons could undertake a task long imagined for nuclear arms: a first strike against another nation’s government or arsenals, interrupting key chains of communication and disabling some of its retaliatory forces, all without the radioactive fallout and special condemnation that might accompany the detonation of nuclear warheads. That’s why a National Academies of Sciences, Engineering and Medicine report said in 2016 that hypersonics aren’t “simply evolutionary threats” to the United States but could in the hands of enemies “challenge this nation’s tenets of global vigilance, reach and power.”

The arrival of such fast weaponry will dangerously compress the time during which military officials and their political leaders — in any country — can figure out the nature of an attack and make reasoned decisions about the wisdom and scope of defensive steps or retaliation. And the threat that hypersonics pose to retaliatory weapons creates what scholars call “use it or lose it” pressures on countries to strike first during a crisis. Experts say that the missiles could upend the grim psychology of Mutual Assured Destruction, the bedrock military doctrine of the nuclear age that argued globe-altering wars would be deterred if the potential combatants always felt certain of their opponents’ devastating response.