NUCLEAR WEAPONS, LIKE the poor, seem likely always to be with us. Even though arms-control agreements between America and the Soviet Union, and then Russia, have drastically reduced overall numbers, both countries are committed to costly long-term modernisation programmes for their strategic nuclear forces that should ensure their viability for the rest of the century.

Russia is about halfway through recapitalising its strategic forces, which include a soon-to-be-deployed road-mobile intercontinental ballistic missile (ICBM); a new heavy ICBM; eight new ballistic-missile submarines (SSBNs), most of which will be in service by 2020; upgraded heavy bombers; and a new stealth bomber able to carry hypersonic cruise missiles. America will replace every leg of its nuclear triad over the next 30 years, at an estimated cost of $1.2trn. There will be 12 new SSBNs; a new penetrating strike bomber, the B21; a replacement for the Minuteman III ICBMs; and a new long-range air-launched cruise missile. As Tom Plant, a nuclear expert at RUSI, a think-tank, puts it: “For both Russia and the US, nukes have retained their primacy. You only have to look at how they are spending their money.”

Other states with nuclear weapons, such as China, Pakistan, India and, particularly, North Korea, are hard at work to improve both the quality and the size of their nuclear forces. Iran’s long-term intentions remain ambiguous, despite the deal in 2015 to constrain its nuclear programme. Nuclear weapons have lost none of their allure or their unique ability to inspire dread. Whether or not they are ever used in anger, they are very much part of the future of warfare.

So far, the best argument for nuclear weapons has been that the fear of mutually assured destruction (MAD) has deterred states that possess them from going to war with each other. MAD rests on the principle of a secure second-strike capability, which means that even if one side is subjected to the most wide-ranging first strike conceivable, it will still have more than enough nuclear weapons left to destroy the aggressor. When warheads became accurate enough to obliterate most of an adversary’s missiles in their silos, America and Russia turned to submarines and mobile launchers to keep MAD viable.

A more dangerous world

It still is, and is likely to remain so for some time. But disruptive new technologies, worsening relations between Russia and America and a less cautious Russian leadership than in the cold war have raised fears that a new era of strategic instability may be approaching. James Miller, who was under-secretary of defence for policy at the Pentagon until 2014, thinks that the deployment of increasingly advanced cyber, space, missile-defence, long-range conventional strike and autonomous systems “has the potential to threaten both sides’ nuclear retaliatory strike capabilities, particularly their command-and-control apparatuses”, and that “the potential of a dispute leading to a crisis, of a crisis leading to a war, and of a war escalating rapidly” is growing.

In a new report, Mr Miller and Richard Fontaine, the president of the Centre for a New American Security (CNAS), identify cyber and counter-space (eg, satellite jammers, lasers and high-power microwave-gun systems) attacks as possible triggers for an unplanned conflict. Other new weapons may threaten either side’s capability for nuclear retaliation, particularly their strategic command-and-control centres. James Acton, a nuclear-policy expert at the Carnegie Endowment for International Peace, lists three trends that could undermine stability in a future crisis: advanced technology that can threaten the survivability of nuclear attacks; command-and-control systems that are used for both nuclear and conventional weapons, leaving room for confusion; and an increased risk of cyber attacks on such systems because of digitisation.

Both America and Russia rely heavily on digital networks and space-based systems for command, control, communications, intelligence, surveillance and reconnaissance (C3ISR) to run almost every aspect of their respective military enterprises. Cyber space and outer space therefore offer attackers tempting targets in the very early stages of a conflict. In the utmost secrecy, both sides have invested heavily in offensive cyber capabilities. In 2013 the Defence Science Board advised the Pentagon that: “The benefits to an attacker using cyber exploits are potentially spectacular. Should the United States find itself in a full-scale conflict with a peer adversary, attacks would be expected to include denial of service, data corruption, supply-chain corruption, traitorous insiders, kinetic and related non-kinetic attacks at all altitudes from under water to space. US guns, missiles and bombs may not fire, or may be directed against our own troops. Resupply, including food, water, ammunition and fuel, may not arrive when or where needed. Military commanders may rapidly lose trust in the information and ability to control US systems and forces.”

One problem with this is that the space architecture on which America depends for its nuclear command and control, including missile early warning, is also used for conventional warfare. That means a conventional attack might be mistaken for a pre-emptive nuclear strike, which could lead to rapid escalation. Another difficulty is that an aggressor may be tempted to go after cyber and space assets in the hope of causing major damage to a target’s defences without actually killing anybody. That would raise doubts over whether nuclear retaliation could be justified. A third worry is that because of the potential speed and surprise of such attacks, some responses might be delegated to autonomous systems that can react in milliseconds. Lastly, there is the possibility of “false flag” cyber operation by a rogue state or non-state hacker group.

Don’t worry just yet

For now, the prospects of a successful disarming strike remain sufficiently remote to leave the strategic balance intact. Mr Miller argues that it would require a “fundamental transformation in the military-technological balance…enabled by the development and integration of novel military capabilities” to upset the balance.

Ominously, he thinks that such a fundamental transformation may now be on the horizon, in the shape of conventional prompt global strike (CPGS) and new missile-defence systems. Both China and Russia fear that new American long-range non-nuclear strike capabilities could be used to deliver a disarming attack on a substantial part of their strategic forces or decapitate their nuclear command and control. Although they would still launch their surviving nuclear missiles, improved missile-defence systems would mop up most of the remainder before their warheads could do any damage.

Still, Michael Elleman, a missile expert at the International Institute for Strategic Studies, reckons that for now those concerns are overblown. As much as anything, he says, they are talked up to restrain investment in the enabling technologies: “They [the Russians and the Chinese] are saying to the US, the trouble with you guys is that you never know when to stop.”

CPGS would involve a hypersonic missile at least five times faster than the speed of sound and a range of more than 1,000 miles. This could be achieved in several ways. One would be to stick a conventional warhead on an ICBM or a submarine-launched ballistic missile—a cheap solution but a dangerous one, because defenders would not know whether they were under conventional or nuclear attack, so they might overreact.

The alternatives would be a cruise missile powered by a rocket-boosted scramjet (a supersonic combusting ramjet) engine, or a boost-glide vehicle that would be launched from a ballistic missile and then fly towards its target like a paper dart. Glide vehicles pull up after re-entering the atmosphere, using the curvature of the Earth to delay detection by ballistic-missile defences. Both types would be manoeuvrable, and would be accurate to within a few metres of their target. However, they, too, could carry nuclear warheads, again leaving the target uncertain what kind of attack it was under. America first tested a glide vehicle in 2010, but seems in no rush to deploy them. Russia and China have more recently tested hypersonic glide missiles.

Current American missile-defence systems, such as Patriot, THAAD (terminal high-altitude area defence) and Aegis, provide quite effective regional defence but are not designed to cope with a salvo of ICBMs. The Ground-based Midcourse Defence system in Alaska and California is supposed to provide some defence of the homeland against a few missiles launched by a North Korea or an Iran, but it was never designed to defeat a massive salvo attack by a major adversary.

However, substantial improvements are on their way. Mr Elleman describes the SM-3 IIA interceptors, which could be deployed as soon as next year on Aegis-class destroyers, as a “big deal”. They are much faster than their predecessors, and Mr Miller thinks that if hundreds of them were put on ships close to America, they might support a late midcourse defence against Russian ICBMs.

More exotic missile defences are not far behind. Mr Elleman says that in about five years’ time it may be possible to put solid-state lasers on large numbers of unmanned aerial vehicles (UAVs) orbiting at very high altitude. Small missiles could also be put on UAVs as boost-phase interceptors, firing a minute or so after launch. Interception at that stage is technically much easier than later on because the target is much larger when all its stages are still intact, and moving more slowly.

Mr Elleman believes that for now the advantage is likely to remain with the attacker rather than the defender, but like Mr Miller he fears that emerging technologies could “undermine crisis stability very rapidly”. Yet if arms-control agreements could be reached at the height of the cold war, it should surely be possible for America, Russia and China to talk to each other now to avoid persistent instability.