Navy Tests Hypersonic Weapons That Could Hit Anywhere on Earth in an Hour
The Prompt Global Strike concept got a boost in the post-9/11 era, when it seemed as if such weapons could be useful to strike fleeting targets such as terrorist meetings, or to take out elusive targets such as Saddam Hussein and Osama bin Laden. (In indeed, an attempt was made to bomb Saddam Hussein at Dora Farms, Iraq before the 2003 invasion, but he was not there at the time.) Nowadays, possible PGS uses include destroying a nuclear missile sitting on a launch stand in North Korea or Iran, targeting weapons of mass destruction in the hands of terrorists, or even hitting targets quickly during a conflict with a state such as China or Russia.
PGS originally took many forms, including a conventional version of the submarine-launched Trident D-5 missile. The problem was that a conventional (non-nuclear) Trident launch looks exactly the same as a nuclear Trident launch. In the heat of conflict an adversary might panic when it detects a Trident missile in flight, not knowing whether it carried a conventional or nuclear warhead. If the adversary also had nuclear weapons, it might be tempted to launch a counterstrike on the erroneous belief it was under nuclear attack.
Now the Navy if trying out "boost glide" hypersonic weapon technology. Hypersonic weapons travel at speeds of Mach 5 10 Mach 10. Boost glide hypersonic weapons typically sit atop a ballistic missile and ride the missile to a great height and speed, before detaching from the missile and gliding down to the target at blistering speed. Boost glide weapons have a different flight profile from ballistic missiles, detaching before the missile leaves the atmosphere, so they're relatively easy to differentiate on a radar screen from a regular ballistic missile that could be carrying a nuke.
Not much else is known about the October 30 test. The U.S. Navy's Strategic System Program, which oversaw the test, told USNI News it was "the first conventional prompt strike missile for the United States Navy" that the Navy could someday deploy on its guided missile and attack submarines. Submarines are ideal platforms for PGS, as they can loiter underwater near targets, whittling down the reaction time even farther. However, Hypersonic weapons are difficult to develop. The faster a weapon flies, the harder it is to steer, making precision targeting difficult. Hypersonic speed also dramatically increases the aerodynamic forces and temperatures (up to 1800 degrees Fahrenheit) the weapon is exposed to. These issues pose immense, but not insurmountable, technical challenges.
The U.S. isn't the only country working on hypersonic weapons. China has tested its DF-ZF hypersonic weapon several times. It and Russia's Yu-71 are both boost glide weapons, though the two countries have their own reasons for developing them. Russia sees the Yu-71 as a way to sneak a nuclear warhead around America's long range ballistic missile defenses, while China could use them to get around shorter range anti-ballistic missile systems such as THAAD and Patriot PAC-3 that protect U.S. bases across the Asia-Pacific. This summer, the California-based think tank Rand Corp suggested the U.S. and other major powers work to limit the spread of hypersonic weapons worldwide on the grounds they are inherently destabilizing. Like conventional Trident, the extreme speed of hypersonic weapons gives a country's leaders little time to react to them, possibly forcing them to use their nuclear arsenals before losing them to hypersonic attack.