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The Case for a New US Tactical Nuclear Weapon

November 19th, 2016

By Dr Rowan Allport – Senior Fellow

If there were ever any doubt that Donald Trump is not secretly an expert in defence and security policy, the illusion that there might be more than meets the eye was dispelled early on in his campaign with his response to a question on US nuclear strategy. When asked by a radio host what his priorities were for regenerating the US nuclear triad – the sea, land and airborne components of the US nuclear deterrent – Trump responded, after much blustering, by saying “I think – I think, for me, nuclear is just the power, the devastation is very important to me”. Clearly, he had no idea what he was talking about. But facing a bill of around $1 trillion for the full regeneration of a force that is many decades old, there is now a need for deep introspection amongst US leaders in not only deciding how the US nuclear force is maintained into the second half of the 21st century, but also exactly what that deterrent should be tasked to accomplish, and if its current form is the one most suited to meet the challenges that lie ahead.

The US strategic deterrent currently consists of three components, with plans already well in hand for their redevelopment. At sea, the US Navy operates fourteen Ohio-class ballistic missile submarines (SSBN) carrying Trident D-5 submarine launched ballistic missiles (SLBM). These are to be replaced by twelve Columbia-class submarines, which will also carry Trident missiles, at a cost of around $100bn. On land, the USAF operates 450 – soon to be reduced to 400 – LGM-30G Minuteman III intercontinental ballistic missiles (ICBMs). These missiles, which date from the 1970s, are to be superseded by a new ICBM model under the Ground Based Strategic Deterrent (GBSD) programme for a projected price of $85bn. The USAF also operates the airborne leg of the triad, which is primarily based upon an inventory of AGM-86 air-launched cruise missiles (ALCM) carried by B-52H bombers. The Air Force envisages that these missiles will be superseded by the Long Range Stand-Off (LRSO) weapon – a $20-30bn cruise missile that will eventually arm the B-52H, B-2A and B-21 Raider bombers, the latter of which is still in development and itself has a programme price tag of over $42bn. Additional strategic capability is currently provided by the B-52H and B-2A bombers – as well as a variety of strike aircraft – that carry the earth-penetrating B61-11 and the high-yield B81 bombs.

Of these three branches, only the SLBM arm is broadly free of criticism due to the unique survivability of submarine-based missiles. In contrast, there is a more diverse dialogue regarding ICBMs. Those against their replacement argue that such missiles represent overkill when SSBNs are available, and that ICBMs are vulnerable to the point to which they have to be ‘launched on warning’ of an incoming nuclear attack, whilst SLBMs can ride out any initial strike. Those in favour of their retention point out that the ICBM force – situated deep in the central US – is essentially invulnerable to conventional attack and would be extremely difficult to destroy using nuclear weapons due to the extent to which their silos are geographically dispersed.

The most poorly supported leg of the triad by far is the bomber-based component. This is not a new development: since the introduction of the ballistic missile, the US bomber force has been in search of ways to justify its existence as a nuclear strike force. There is little doubt that crewed bombers carrying long-range nuclear cruise missiles offer considerable mission flexibility, particularly in allowing the use of strategic nuclear weapons in a manner that falls short of a civilisation-ending ballistic missile exchange. Those opposed to the LRSO programme, however, claim that such weapons provide a level of redundancy that simply cannot be justified, and that the possession by the US of both nuclear and conventionally armed cruise missiles presents the prospect of a nuclear war being accidentally triggered.

A great challenge with nuclear strategy is linking capability to potential (and acceptable) real world scenarios. During the Cold War, the trigger for a nuclear conflict was anticipated to be a war between NATO and the Warsaw Pact in Europe that would eventually become nuclear in nature. The question then would be whether the exchange stayed relatively localised or escalated into a global war. Filling this gap between conventional war and an all-out strategic exchange would have been the use of tactical nuclear weapons.

No hard and fast definition of tactical, or sub-strategic, nuclear weapons exists. Generally, they are less powerful than their strategic counterparts, shorter range and are designed to be used either on the battlefield or against targets in close proximity to them. However, many have a higher yield than the weapons that destroyed Hiroshima (~15 kilotons (kt)) and Nagasaki (~21 kt); they often possess a range dependent on the launch method; and whether a target is strategic or tactical often has more to do with perception than objective fact. In a similar vein, it has been claimed that it is not possible to distinguish between tactical and strategic nuclear warfare, or that the former will escalate into the latter in a manner that is uncontrollable. Nevertheless, such arguments – some of which depend on dubious interpretations of questionable wargame exercises – do not erase the political and military impact the existence and use of such weapons can have.

Historically, such sub-strategic weapons have ranged in form from nuclear artillery shells and short-range missiles to depth charges and a vast array of free-fall bombs. To the US and USSR, these weapons presented a compromise that allowed for the most intense conflict imaginable to be fought in Europe without a resort to mutual destruction. For NATO as a whole, tactical nuclear weapons also provided a response to overwhelming Soviet conventional force numbers.

With the break-up of the USSR, the post-Cold War era has seen the effective elimination of all but around 500 freefall bombs from the US’s tactical nuclear arsenal. However, Russia – whilst also cutting back on its stockpile – retains a large tactical nuclear force, with estimates suggesting that Moscow possesses just under 2,000 operational sub-strategic warheads, albeit stored in a centralised location. The recent transfer of nuclear-capable Iskander-M short-range missiles – a weapon to which NATO has no equivalent – to the Kaliningrad Oblast indicates that such systems still play a major role in Russian military thinking. In truth, the concept of the use of nuclear weapons to “de-escalate” a conventional war in which Russia is at risk of being overwhelmed is a central part of its defence doctrine. A caveat to this, introduced in 2010, is that only in a scenario in which “the very existence of the state is under threat” can such weapons be used. However, the increasing personalisation of the state under the leadership of Vladimir Putin means that the continued rule of one man could soon become synonymous with state survival amongst Russia’s security elite – if this is in fact not already the case. There is, therefore, a need to be able to offer a credible and proportionate response to a limited use of nuclear weapons by Moscow.

The issue of the need for sub-strategic nuclear options is even more acute in Southeast Asia. Here, both the challenge of nuclear weapons use and the issue of overwhelming conventional force remains very much present. North Korea has an expanding nuclear arsenal, but it is (thankfully) difficult to imagine that any act of war – even a nuclear attack on US assets – by a still comparatively weak Pyongyang would compel a US president to exterminate potentially millions of civilians in a strategic nuclear strike on the country. More limited nuclear options are, therefore, required for the US deterrent umbrella to be credible.

China itself would be even more of a challenging prospect. Whilst North Korea has a relatively antiquated air defence system, China can project an A2AD bubble far beyond its borders. The threat of a Chinese invasion of Taiwan could ultimately see troop landings along the Taiwanese coast that were protected by A2AD assets securely stationed within China. In such a scenario, it might be necessary for the US to resort to a limited use of nuclear weapons to halt such a landing. Again, such an action would have to be both plausible to act as a deterrent to Beijing initiating a conflict in the first place and in providing options in the event of war.

In both the European and Southeast Asian context, tactical nuclear weapons also have a role in providing credible reassurance to US allies. A dedicated and viable sub-strategic force allows the US to demonstrate that it is serious about retaining a realistic nuclear fallback option. Claims that the Japanese Government was unnerved by the US decision to scrap the submarine-launched nuclear variant of the Tomahawk missile remain unconfirmed, but would certainly tie in with what would be a common sense worry from Tokyo that a reduction in US nuclear flexibility signalled parallel reductions in a willingness to count nuclear weapons as an option in its allies’ defence.

Current US efforts to modernise its tactical nuclear force centre almost exclusively on the B61 bomb upgrade programme. The $8.5bn scheme is seeing four models of the 1960s-era free-fall weapon upgraded to the B61-12 standard – a process that involves them being fitted with an internal guidance system, an earth-penetrating option, a (limited) standoff capability, as well as an improved flexibility of explosive yield. This programme will also lower costs through the retirement of five existing weapons (the existing B61-3, 4, 7, and 10 models plus the high-yield B83 bomb). In the event of actual use, lower collateral damage due to the enhanced precision allows for a lower warhead yield: the B61-12 has a maximum setting of 50 kt, compared to the B61-7’s 360 kt. Whilst not a pure tactical weapon – if, as noted above, such a thing could ever exist – it is the closest thing the US will possess for the foreseeable future.

Unsurprisingly, there have been vocal objections to the B61-12 programme from many quarters, with concerns ranging from cost to the inherent increase in instability the deployment of a more ‘usable’ nuclear weapon could bring. Resistance has been compounded by the fact that many of these weapons will be based in Europe as part of the wider NATO deterrent. However, there are also more practical issues concerning how such weapons would be employed. It is very unlikely that the US would ever conduct a nuclear strike against a state that did not possess a potent air defence capability. Even if carried by an F-35 or B-2A there would be challenges: contrary to popular belief, stealth technology has serious limitations when used in isolation, and is far from perfect even in ideal conditions. Flying hundreds of miles into defended airspace to drop a bomb more or less directly over the target presents a high probability of mission failure – particularly if it is attempted early on in a conflict before attrition has been inflicted on enemy air defences. The B61-12 is touted as having a standoff capability, but its range has been kept classified. However, being an unpowered weapon without glide wings, it is unlikely to be able to travel significantly further than the similarly configured JDAM – around 15 miles when launched in ideal conditions.

The B61-12 upgrade should, therefore, be seen to be what it really is: a programme to extend a limited capability at an affordable price. In this sense, it is perfectly justified. However, what if there were a path forward that could deliver a more viable tactical nuclear capability without the need for new money?

Step forward once again the LRSO weapon. As already highlighted, this is the most controversial of the US nuclear triad recapitalisation efforts. Much like the B61-12 upgrade, there are also valid questions as to what would be delivered for the price tag. The LRSO weapon is broadly described as being a subsonic stealth cruise missile, but that sounds very much like a reincarnation of the 1980s vintage AGM-129A Advanced Cruise Missile that was retired in 2007, and not a great deal further along than the AGM-86 it is intended to replace. Most of the alleged upgrades – enhanced range, retargeting capability and more accurately selectable warhead yield – are tweaks rather than leaps forward. Claims that the missile could have a sub-strategic role are credible, but survivability remains an issue. Additionally, much of the psychological value of genuine tactical nuclear weapons is derived from them being specifically designed for such a role – a makeshift capability from a primarily strategic weapon does not provide this to anything like the same extent.

If the LRSO weapon genuinely represented a game-changing system that perhaps incorporated hypersonic speed there might be a better case to be made, but investing tens of billions of dollars for little improvement on an already vulnerable delivery concept is hardly enticing. There is also the valid question of why the USAF is spending tens of billions on the B-21 Raider bomber programme if the aircraft needs to be able to hold back 1,500 miles (the likely minimum range of the LRSO weapon) from the target.

Therefore, what might a better alternative to the LRSO be? It would primarily have to perform a distinct function. This should be to provide a survivable tactical nuclear capability. It would also have to leverage platforms currently in development, most notably the B-21; not be strategically destabilising; and not require any technological breakthrough, so as to avoid becoming a money pit. The best solution would, therefore, see the USAF develop an air-launched, Mach 3+ standoff weapon with a range of around 300 miles and a warhead of no more than 50 kt. A range and warhead this limited would allow the delivery platform to stay out of the likely reach of any air defences whilst avoiding the destabilising effect of a new strategic weapons system. Additionally, capping the range would make delivering the necessary speed possible without resort to exotic technology. Such a missile would have a far greater prospect of success in an A2AD environment than any other non-ballistic system available or planned, and with a capability that was designed specifically for tactical use, it would send a potent signal of intent.

The US has fielded similar weapons in the past. The AGM-69 Short Range Attack Missile (SRAM) – in service from 1972-1993 – was a straightforward supersonic missile with a range of around 115 miles and a warhead with a yield of up to 210 kt. It even had a planned successor: the AGM-131A SRAM II was a similar missile with a variety of upgrades including a range that was extended to 250 miles. However, the programme was cancelled in 1991. Neither of these weapons were designed for tactical use: rather, they were intended to hit air defence sites on the perimeter of the USSR. Nevertheless, the basic concept remains viable for use against non-strategic targets. In a similar vein, France currently deploys the Air-Sol Moyenne Portée-Amélioré (ASMP-A), a supersonic ramjet-powered missile with a range of around 300 miles and a warhead with a yield of up to 300 kt. It should be well within the ability of US industry to replicate these efforts, and there is the possibility of such a missile also having a conventional warhead variant.

The path to cancelling the LRSO weapon is fraught with not only the genuine arguments in favour of the programme, but also issues of economics, politics, prestige, legality and engineering. At the commercial level, there are workarounds: much of the economic momentum behind the programme is based on the assumption that it will be cancelled and replaced with nothing. A commitment to ‘SRAM-Next Generation (NG)’ would likely mitigate these fears. Politically, cancelling any weapons in the face of members of Congress with constituents’ jobs on their minds is a major task.

The prestige issue is less tangible, but potentially more difficult to deal with. Scrapping the LRSO weapon would in large part end the role of the USAF bomber force in the country’s strategic deterrent. Whilst the B61-7, B61-12 and SRAM-NG would allow the US bomber force to retain a nuclear role, it would be perceived to be second tier – even if that tier was actually of greater operational relevance than the surviving arms of the triad. However, the expenditure of tens of billions of dollars for a broadly superfluous system cannot be justified when there are other priorities: the US Navy lost its battleships as their utility faded, and the USAF must now face up to a similar situation.

At the international level, a quirk in the New START treaty – which currently governs US and Russian nuclear weapons possession – means that whilst individual warheads on missiles are counted towards the limit of 1,550 deployed weapons each, a bomber is counted as a single warhead however many weapons it is carrying. In practice, this means that a B-52H carrying twenty ALCM is only counted as a single weapon, and that abandoning such systems could effectively reduce the number of strategic weapons the US can possess. However, given that this treaty is due to expire in 2026 even if it runs to its full potential length, scope exists to renegotiate this provision in any successor treaty. It could also potentially spur an effort to eliminate long-range nuclear standoff weapons across the world.

Finally, there would also be technical challenges: the USAF has selected the W80 warhead from the existing cruise missile force to be upgraded to W80-1 standard and installed on the LRSO weapon. Whether this warhead would be robust enough to survive a Mach 3+ journey on a SRAM-NG is open to question. An alternative warhead, based on the B61-derived W85 devices carried by the now retired Pershing II missile, would likely prove more resilient, but concerns persist about having too many nuclear weapons based upon the B61 design. Nevertheless, it is difficult to believe that a path around these difficulties could not be found in relatively short order.

The technicalities – and even more so the practicalities – of nuclear strategy are distasteful to many. There is, however, a need to examine the details of the problem in order to identify the middle ground between simply writing off nuclear weapons as indescribably evil and maintaining a zombie-like attachment to maintaining the status quo. The US should now seek to assess the purpose for which it is sustaining its nuclear force not just in the context of symbolism, but for the practical value it can provide to the defence of its interests.

Picture: A B-61-12 prototype – credit USAF

About Rowan Allport

Dr Rowan Allport is a Senior Fellow who leads the HSC's Security and Defence team. Rowan holds a PhD in Political Science and an MA in Conflict, Governance and Development from the University of York, as well as a BA (Hons) in Politics, Philosophy and Economics from the University of Hull. Specialising in strategic analysis and international security, Rowan's primary areas of interest lie in the defence issues in and around the NATO region, interstate conflict and US foreign policy discourse. He is also the lead author of HSC's recent The Two Per Cent Solution: an Alternative Strategic Defence and Security Review report. Rowan's publication credits include articles and commentary in The Diplomat, The Hill, DefenseOne, RealClearDefense, The Strategist, UK Defence Journal, Politics.co.uk and The National Interest.