THE INTERCONTINENTAL BALLISTIC missile (ICBM) took off from Kwajalein Atoll in the middle of the Pacific Ocean on November 17th. American satellites spotted its bright plume at once. They alerted Schriever Air Force Base in Colorado which in turn informed the USS John Finn, an Arleigh Burke-class destroyer poised north-east of Hawaii. A hatch on the deck flipped open and spewed out a torrent of flames as an SM-3 Block IIA interceptor shot up and out. High above the Earth, it collided with the descending ICBM.
It was the first time an interceptor fired from a warship had shot down a (mock) ICBM in space. “Politically this test is a big deal,” says James Acton of the Carnegie Endowment for International Peace, a think-tank. Russia and China have always complained that American missile defences undermine their own deterrents. America has always batted away those concerns. When the SM-3 was developed, America first said it would protect aircraft-carriers, and later that it would shield Europe from Iranian medium-range missiles. In fact, only a software tweak was needed to make it work against longer-range ones. Now that the system has been demonstrated against an ICBM, both Russia and China will claim vindication.
America already has a missile shield for its homeland, comprising 44 ground-based interceptors (GBIs) in Alaska and California. These were previously the only ones to have shot down an ICBM. Yet these are staggeringly expensive, relatively few in number and unreliable in tests. The ship-based system, known as Aegis Ballistic Missile Defense (BMD), has several advantages. It can be rolled out more quickly, moved where needed and allows America to field many more interceptors.
Currently, 44 destroyers and cruisers are equipped with Aegis BMD. Each has 90-plus launch tubes, so several thousand interceptors could theoretically be put to sea (in practice, the tubes also carry other weapons, like Tomahawk cruise missiles). The navy plans to fit Aegis to 65 ships, 11 of which would be allocated for the protection of the continental United States. Just three to four ships deployed off America’s coast could cover its whole landmass, notes George Lewis, a missile-defence expert who recently retired from Cornell University. The idea is that if GBIs failed to take out a missile, Aegis could mop it up at a lower altitude—though SM-3 IIAs can still reach three times higher than the International Space Station.
In practice, notes Mr Acton, intercepting an incoming ICBM would still be forbiddingly difficult. They would travel a longer distance and therefore arrive at greater speed than in the test, armed with counter-measures to trick the interceptor and potentially in sufficient numbers to overwhelm defences. “SM-3 IIAs can’t fundamentally undermine China’s or Russia’s nuclear deterrents, or even frankly North Korea’s,” he says. But that is not how those countries are likely to see the matter.
Russia has long held that arms-control talks ought to include not just offensive systems, like bombers and missiles, but also defensive ones which might neuter them. It has been especially irked by land-based Aegis systems built in Romania and Poland. The new test “is likely to have a crushing effect on prospects for new nuclear arms control agreements”, says Laura Grego of the Union of Concerned Scientists, an advocacy organisation.
“It will also provide motivation (or justification) for Russia and China to diversify and grow their nuclear weapons arsenals,” she adds—the logic being that more missiles will be needed to saturate stiffer defences. China is especially jittery as it has relatively few land-based ICBMs.
Ms Grego notes that because the SM-3 interceptor can also take out satellites—something America demonstrated in 2008—deploying more of them will have an impact on space security, too. But with the Iranian and North Korean nuclear programmes simmering, the incoming Biden administration is not about to abandon a flexible seaborne means of shielding its European and Asian allies.