On February 2, the Trump administration released a new Nuclear Posture Review (NPR). The 2018 NPR commits to maintaining and modernizing the U.S. nuclear triad — intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and strategic bombers — and positioning dual capable aircraft (DCA) that can be deployed globally as an important element in the extended deterrence toolkit.
In addition, the 2018 NPR decided to strengthen the flexibility of U.S. nuclear force structure, especially with two low-yield nuclear options, the low-yield Trident D5 SLBM and the new sea-launched cruise missile (SLCM) as a follow-on system of the nuclear variant Tomahawk (TLAM-N), which was retired following the 2010 NPR.
The 2018 NPR explains the primarily role of these systems as deterrence against a limited use scenario by Russian intermediate-range nuclear forces (INFs) or other non-strategic nuclear forces. This assessment is correct, but these sea-based systems have global impact. In other words, they also have a very important meaning in the tailored deterrence posture in Northeast Asia.
Rapid Deployability of DCAs and Its Crisis Stability Problem in Asia
According to the 2010 NPR, the role of the retired TLAM-N could be substituted by strategic bombers and globally deployable DCAs. Certainly, these aerial assets can deliver a B61 variant, one of the existing low-yield nuclear bombs, and its visibility is effective as a deterrent signal. In addition, bombers with air-launch cruise missiles such as the AGM-86B and its follow-on system, Long-Range Standoff (LRSO) weapons will provide the essential flexibility for a regional tailored deterrence posture.
However, given the increase in theater-range missile threats from North Korea and China — which may be used as anti-access/area-denial measures — the United States and its allies will need to re-evaluate the risks of deployment of DCAs to nearby forward bases such as Misawa or Kadena in Japan, Kunsan or Osan in South Korea, and even Andersen Air Force Base in Guam, when military tensions rise.
In addition, since U.S. dual capable stealth assets are hard to detect and intercept in the air, adversaries have an incentive to use their theater-range strike capabilities early on in a confrontation to counter perceived U.S. advantages in power projection. This is because detection and neutralization have a much higher probability of success while such assets are on the ground.
The vulnerability of DCAs and the probability of undermining crisis stability is one of the reasons why it is inappropriate for Japan and South Korea to adopt a NATO-type nuclear sharing arrangement. Especially if B61 nuclear bombs must be stocked in a hardened ammunition depot like in Kleine Brogel Air Force Base in Belgium and Buchel Air Force Base in Germany, the incentive for adversaries to launch a first strike on these nuclear weapons will increase.
As was the case in Europe during the Cold War, the NATO allies, especially the nuclear sharing host nations, bear a risk of entrapment. However, the major difference with Asia is that DCA and tactical nuclear weapons are already deployed in Europe, while it is only a possibility that they will be deployed as a contingency or during a crisis in the Asia-Pacific region.
Signals sent by having nuclear assets already in place during peacetime and signals of assets developed and detected in a crisis will have different effects on an enemy’s threat perception. This is an important point when considering crisis stability.
North Korea has started dismantling its nuclear test site at Punggye-ri and missile-engine test site at Sohae, but these are reversible and mobile missiles can be launched from anywhere. If North Korea restarts and repeats missile launches and nuclear tests, as in 2017, is it still “peacetime”? Is DCA still forward deployable? If we cannot answer these questions, the reintroduction of U.S. tactical nuclear weapons in South Korea and nuclear sharing with Japan and South Korea through DCAs will not be valid deterrent options.
Roles of Low-Yield, Flexible, and Survivable Nuclear Options in the Asia
On the other hand, it is essential that the combination of long-range standoff missiles and strategic bombers fills the gap in the escalation ladder following the retirement of the TLAM-N. This maintains the flexible option of launching a low-yield cruise missile over 2,500 km from a position west of Guam. In August 2016, the U.S. Air Force awarded approximately $900 million in contracts to Lockheed Martin and Raytheon for 54-months of technology maturation and risk reduction. While the forward deployability of DCAs is being undermined, it is good for the reliability of the extended deterrence force mix that the LRSO program is proceeding smoothly.
Regarding the Ground Based Strategic Deterrent (GBSD) program to develop the follow-on system to the Minuteman III ICBM, some said that the replacement should be canceled due to the vulnerability of silo-based missiles. Others argue that ICBMs are too easy to fire in response to a false alarm, and thus can compromise crisis stability. There is also the issue of budget allocation when compared with other high priority modernization programs such as the F-35, B-21 (a long-range strike bomber under development), and KC-46 (new aerial refueling tanker) in the U.S. Air Force.
Nevertheless, the 2018 NPR and high-ranking defense officials seem to think that the GBSD should be maintained as one leg of the next-generation nuclear triad, along with the Columbia-class ballistic missile submarine and B-21.
For allies, in terms of reassurance and signaling to enemies, the importance of the forward deployability of strategic bombers and DCAs tends to be emphasized. Indeed, it is important, but underwater-based, survivable low-yield options have different roles and characteristics than aerial assets.
According to the NPR, these low-yield options are not intended for “nuclear war-fighting.” Indeed, if the quantity of low-yield D5s can be kept to a small number, it is impossible to uses these to launch a full first strike against Russia and China’s second-strike capabilities. It is just another option in the flexible escalation control toolkit.
However, while the 2018 NPR emphasizes the United States’ substantial counterforce capabilities and describes the specific tailored deterrence strategies for each country, demand for these low-yield weapons seems to have been considered based on capability assessments through some classified war games and specific nuclear operational plans. Considering counterforce targeting, in view of the fact that the nuclear forces of China and North Korea are composed mainly of transporter erector launcher (TEL)-based road-mobile systems, it makes sense to target assets such as mobile launchers and their shelters, or hardened silos.
Only ICBMs or SLBMs could conduct a disarming attack on these hardened or time-sensitive targets. However, the nuclear warheads currently tipped on Minuteman III and Trident D5 missiles have very high yields of at least 100 to 300 kilotons to destroy hard targets. If a high-yield surface burst occurs it will involve a large amount of fall-out, so the missiles cannot be easily used for counterforce without collateral damage.
The Minuteman III can also upload a low-yield warhead, but the ICBM is restricted in its trajectory because the launch site is limited to the U.S. homeland. If the Minuteman III is aimed at target at Eurasia, it will inevitably pass through Russian airspace en route, and there is a possibility that its third-stage motor will fall in that area. Such an incident could be misunderstood as a nuclear attack against Russia, and in the worst case, it may cause Russia to launch nuclear retaliation upon warning.
By contrast, a low-yield SLBM can be launched from anywhere in the ocean, taking advantage of its high accuracy and long range to choose a trajectory that avoids misunderstanding. Furthermore, if ballistic missile submarines approach the target before launch, they can shorten the time to impact, and reliably penetrate the adversary’s air defense.
The low-yield option (0.3 kilotons) of the existing B61 is to be replaced and integrated with the new B61-12 in the mid-2020s. Also, the LRSO will install variable-yield warheads. However, as already pointed out, these weapons systems are delivered by DCAs and strategic bombers; their response would be too slow to carry out disarming strikes against time-sensitive or deeply buried targets. For tactical fighter aircraft to reach North Korea, it takes an hour from Japan and more than 20 minutes from South Korea. But a Trident SLBM launched from Guam’s ocean, should be able to destroy North Korean targets within 18 minutes.
Under the current strategic environment, the targets that might need immediate disarming are North Korean road-mobile ballistic missiles. This includes medium-range ballistic missiles such as the Nodong, Scud-ER (able to attack Japan), intermediate-range Hwasong-12 (which puts Guam within range), and Hwasong-14/15, North Korea’s ICBMs. Generally, liquid fuel for ballistic missiles is difficult to handle, so fuel injection is done just before launch; in that sense, liquid fuel missiles are considered to have less readiness. However, there is an indication that North Korea has strengthened fuel injection capabilities inside shelters and tunnels, reducing the time needed to move and erect the missile outside. Even for these liquid fuel missiles, then, the United States needs the option of an immediate response. In addition, North Korea has already finished developing at least one solid fuel missile, the Pukguksong-2 medium-range ballistic missile.
Although a crisis on the Korean Peninsula is not a desirable situation for Japan, it is necessary to consider various counter measures including a nuclear first use option in order to destroy the North Korean road-mobile missile bases or the missile itself.
The speed of a sea-launched cruise missile is inferior to that of an SLBM. However, unlike air-launched cruise missiles, a sea-based platform can remain in a specific area for a certain period of time and move closer to the target. Plus, compared to a ballistic missile, it is an advantage that cruise missiles can change their target information after launch. It is also possible to supplement the limited number of ballistic missile submarines with other nuclear-powered attack submarines to distribute potential vulnerabilities. In this regard, the Virginia-class Block V with additional vertical launch systems, here the Virginia Payload Module, would play an important role.
Theoretically, it is possible to equip a surface ship with a SLCM. Given advanced threats from anti-ship ballistic missiles (like China’s DF-21D and DF-26) and hypersonic anti-ship cruise missiles, surface ships are too vulnerable to act reliably as a platform for nuclear SLCMs. In addition, usually Aegis destroyers need to equip various weapon systems for integrated air and missile defense missions. Therefore, the new SLCM, like the retired TLAM-N, should be installed on attack submarines.
Taken together, although the stated role of the nuclear SLCM is to raise Russia’s opposition to the INF treaty violation, in reality it is a flexible option to deter North Korea and China, and it plays an important role in reassuring East Asian allies, including Japan.
The 2018 NPR does not deny the possibility of deploying DCAs and non-strategic nuclear weapons in Northeast Asia, but in view of the anti-access/area denial environment, which is expected to become more severe in the future, it seems to hard to continue to identify these as deployable assets. As a result, it is expected that the U.S. nuclear forces in the Asia-Pacific region will tend to rely on submarine-based systems. However, it should be noted that the U.S. submarine forces already have many duties — not only as a nuclear deterrent, but also in the conventional domain, such as land attack missions, anti-submarine warfare, intelligence, and special operation support.
In order to maximize the deterrent effect and its potential efficiency of the low-yield SLBM as a flexible prompt strike capability and the nuclear SLCM, which is relatively slower and shorter-ranged than an SLBM, U.S. allies including Japan should share the burden and firmly conduct anti-submarine warfare in the surrounding waters, to assure that the United States’ submarine force can focus on its deterrent mission and prompt strike capability, if deterrence fails.
Masashi Murano is a Research Fellow at the Okazaki Institute (Tokyo). He is responsible for nuclear/conventional deterrence and missile defense related analysis and, for the past nine years, has been involved in research, analysis, TTX, and facilitation of numerous classified products related to strategic intelligence assessment and policy planning for the Government of Japan and think-tank community.