NORTH KOREAN REGIONAL MISSILE THREAT

North Korea has diligently amassed a very large arsenal of short-, medium-, and intermediate-range ballistic missiles that can reach all parts of the Asia-Pacific region. The bulk of its arsenal consists of short-range Scud-type missiles (see Table 1), which are deployed throughout the country (Sankaran and Fearey Reference Sankaran and Fearey2017, 5–6). North Korea also has a substantial number of Nodong missiles with an approximate range of 1,300 kilometers and a limited number of intermediate-range ballistic missiles (see Table 1).

Table 1 North Korean Short-, Medium-, and Intermediate- Range Missile Specifications

Data from: Bennett Reference Bennett, Crawford and Moon2000, 185; Bermudez Reference Bermudez2001 276 and 289; Cepek Reference Cepek2005, 23; Elleman Reference Elleman2017. “Musudan (BM-25),” Missile Threat, CSIS Missile Defense Project. https://missilethreat.csis.org/missile/musudan/; “Hwasong-7 (Scud ER Variant),” Missile Threat, CSIS Missile Defense Project, https://missilethreat.csis.org/missile/hwasong-7/; Missile Defense Advocacy Agency 2017; National Air and Space Intelligence Center (NASIC) 2017; Nuclear Threat Initiative 2013; Japan, Ministry of Defense 2017; Pinkston Reference Pinkston2008, 30, 50, and 51; Federation of American Scientists 2000; Bermudez Reference Bermudez2011; Nuclear Threat Initiative 2014;

All these missiles are capable of reaching the US and allied targets throughout the Asia-Pacific region. North Korean missiles, when armed with conventional, chemical, or biological warheads, could pose a military threat to major cities, military targets, and forward-deployed US forces and assets.Footnote ³ Biologically armed missiles, for instance, could “rival small nuclear weapons in their ability to kill people” (Fetter Reference Fetter1991, 26).Footnote ⁴ Similarly, North Korean missiles armed with chemical warheads could pose a particularly effective threat to military forces. The impact of a chemical weapon on a military base “is likely to send everyone into protective gear and seriously impair operations” and delay deployments of troops and equipment to the combat zone (Rubenson and Slomovic Reference Rubenson and Slomovic1990, 22 and 23). The same missile impacting a city could cause “40 to 700 times as many deaths, and 20 to 300 times as many injuries, as would result from the same missile armed with a conventional warhead” depending on the prevailing weather and other conditions (Fetter Reference Fetter1991, 21 and 22). Finally, conventionally armed missiles can delay military deployments if they destroy runways or naval berths. Repairing runways, aircraft shelters, naval berths, and other related equipment can take many days.

The United States and its allies consider these potential North Korean missile threats a very potent and immediate concern. Daniel R. Coats, the Director of National Intelligence, said at a Senate testimony in May 2017 that

South Korean and Japanese officials also echo similar concerns.Footnote ⁵

IMAGINING THE NATURE OF A NORTH KOREAN MISSILE CAMPAIGN

North Korean leaders seem to believe that they can coerce South Korean, Japanese, and American decision-makers in a regional contingency using missiles.Footnote ⁶ Since the 1990s, North Korean defectors have warned about the missile threat suggesting that “Pyongyang will try to neutralize the bulk of friendly combat forces positioned near the Demilitarized Zone, derail the South's mobilization and American augmentation efforts” to force a negotiation quickly (US Defense Intelligence Agency 1991, 4–5).

In a 1997 congressional testimony, North Korean Col. Ju-Hal Choi said that

These tactical preferences have persisted to this day.Footnote ⁷ In 2017, the former deputy chief of mission at the North Korean embassy in London informed in a US congressional hearing that if North Korea perceives an imminent attack it “would trigger automatic retaliation, with the North unleashing artillery and short-range missile fire” on South Korean and US forces (Pennington Reference Pennington2017; see also Fisher Reference Fisher2013).

There are currently close to 30,000 US servicemen stationed in South Korea as part of the US Force in Korea (USFK). In a conflict, these front-line troops may need to be augmented with as much as “690,000 ground, naval, and air force troops, 160 vessels, and 2,000 aircraft” (Ministry of National Defense 2016, 53).Footnote ⁸ Rather than waiting for such a massive force to be assembled and a Desert Storm-style operation “suddenly unleashed in high tempo” against it, North Korea seems to be willing to pre-empt if its survival is at stake (Swicker Reference Swicker1998, 10).

In trying to disrupt or delay the arrival of US troops, North Korea may use its ballistic missiles at the early stages of conflict to target major ports and air bases. In South Korea, Pusan and Chinhae naval bases and Osan and Kunsan air bases will be vital bases out of which the United States and allied Navy and Air Force will operate and within the range of North Korean missiles. In Japan, Yokosuka and Sasebo naval bases are viable targets within the range of North Korean missiles. A missile campaign aimed at these targets would derail or delay the arrival of these augmentation forces and significantly alter the course of a conflict.

A North Korean Foreign Ministry spokesman has also suggested that North Korea will consider attacking major cities in addition to military bases in Japan if it is “hostile towards the DPRK following the US” (Watanabe and Koike Reference Watanabe and Koike2018, 81). The North Koreans could also fire a few missiles at major commercial ports to intimidate the political leadership in Japan to stay out of a conflict. Given that Japan “relies on imports for 94 percent of its primary energy supply and 61 percent of its calorie intake,” any disruption in the inflow of goods would cause substantial domestic political turmoil (Schoff Reference Schoff2009, 7).

However, it is important to note that these ballistic missiles tactics are an ambitious agenda, even for an advanced military power. It will certainly not be easy for North Korea to execute an effective missile campaign. Also, US and allied retribution for such actions may weigh heavily against such a missile campaign. However, as Cha writes: “it is possible to be both rational and belligerent … North Korean brinkmanship may be dangerous and escalatory, but from their perspective, it makes sense”(Cha Reference Cha2010). It is conceivable that North Korea might employ its ballistic missile if its vital interests are perceived to be challenged.

MISSILE DEFENSE ASSETS IN THE ASIA-PACIFIC

Regional missile defenses are essential to providing limited protection to US forward-deployed forces, allied forces, and other military and civilian targets in the Asia-Pacific region against the potential North Korean missile campaigns discussed in the previous section. The United States operates most of the missile defense systems in the region. Japan retains a limited ability to perform missile defense operations (Sankaran Reference Sankaran and Kelleher2016, 31–43). The United States, Japan, and South Korea also deploy PATRIOT terminal missile defense system in the region.

The United States deploys two types of missile defense systems in the region, THAAD and BMD-capable Aegis ships equipped SM-3 IA/B missile defense interceptors. The US Army has two THAAD batteries in the region (see Table 2). One THAAD battery is forward-deployed to Andersen Air Force Base (AFB) in Guam to protect vital military assets. A second THAAD battery was recently deployed to South Korea (Shim Reference Shim2017).

Table 2 US Missile Defense Systems in the Asia-Pacific

Data from: Syring Reference Syring2016, 53 and 65; Doyle Reference Doyle2017, 14; McKeon Reference McKeon2016, 14; Missile Defense Advocacy Agency 2018; Werner Reference Werner2018; Syring Reference Syring2017, 46; Graves Reference Greaves2019, 27 and 34.

The US Navy has forward-deployed eight BMD-capable Aegis ships (1 Ticonderoga Class Guided Missile Cruisers (CGs) and 7 Arleigh Burke Class Guided Missile Destroyers (DDGs)) to the region (see Table 2). However, two of these eight forward-deployed ships are not on active duty. The USS John S. McCain (DDG-56) and USS Fitzgerald (DDG-62), were damaged in accidents in 2017 (Navy Office of Information 2017). Both these ships are still undergoing repairs, sea trials, and testing (LaGrone Reference LaGrone2019a, Reference LaGrone2019b). Consequently, only six of the eight BMD-capable Aegis ships are now available for combat operations. Additionally, in a contingency, Aegis ships are often needed for other priority missions. Assuming two of the six Aegis ships currently available need to be dedicated to other missions, four ships will be available for missile defense patrols if a situation arose shortly.

While eventually Aegis ships stationed in other parts of the world might be surged to provide reinforcements, it will take anywhere from 10 to 30 days to route other ships to the Asia-Pacific region (Cole Reference Cole, Swaine, Yang, Medeiros and Mastro2007, 197). Additionally, the actual missile defense capabilities of a ship not only depend on the number of available ships, but also on the number of interceptors loaded into the ships.Footnote ⁹ Depending on mission parameters, between 16 and 35 SM-3 IA/B interceptors are usually loaded onto a BMD-capable Aegis ship (Clark Reference Clark2014, 19; Swicker Reference Swicker1998, 36 and 43; Gunzinger and Clark Reference Gunzinger and Clark2016, 6).

PERFORMANCE OF MISSILE DEFENSES AGAINST NORTH KOREAN REGIONAL MISSILES

Two sets of simulation experiments were conducted to determine the defensive capabilities of US forward-deployed and allied missile defense assets. The mechanics of the simulation experiments are based on a combination of mixed-integer linear optimization and missile aerodynamics (Brown et al. Reference Brown, Carlyle, Diehl, Kline and Wood2005).Footnote ¹⁰ These simulations are often used by the military operations research community to study combat tactics. However, I have repurposed them to explore the impact of missile defenses on strategic stability. These simulations are designed to test the proposition that missiles currently deployed by the US, and its allies are reasonable and necessary to defend against North Korea. The evidence obtained using the simulations will fill a critical gap by linking empirical estimation of the adequacy of the defense to the debate on missiles defenses and strategic stability.

In the simulations, sixteen different launch sites spread across North Korea are modeled to ensure geographical dispersion. Each launch site has a limited inventory of various North Korean missiles (see Table 1). Further details on the launch and target sites are included in the online appendix. The performance parameters of the various North Korean missile can be found in Table 1, and the performance parameters of the various missile defense interceptors are included in the online appendix.

In the first simulation experiment, a simplistic threat is modeled to determine the ability of PATRIOT batteries to provide a defense to South Korea. Some Chinese officials and analysts have suggested that certain “US tactical BMD systems are not destabilizing” as long as there is a clear distinction between those tactical systems and strategic BMD systems (Riqiang Reference Riqiang2013, 45). These individuals note that they neither oppose “genuine TMD [Theater Missile Defenses]” nor “deny any country the right of self-defense” (Diamond Reference Diamond1999, 27; Lars Reference Lars2007, 169; Medeiros Reference Medeiros2001, 11). In most cases, it seems that the tactical system they have in mind is the PATRIOT terminal missile defense system. Therefore, the first simulation tests the ability of PATRIOT batteries to provide an effective defense to South Korea. A single missile is fired at six sites in South Korea (see Table 4 in the online appendix for a list of target sites). PATRIOT batteries are emplaced at each of the six targeted sites. As Figure 1 shows, PATRIOT missile defense batteries can kinematically intercept North Korean ballistic missiles targeting each of the six sites, if the missiles fly on a minimum energy trajectory.Footnote ¹¹

Figure 1 Performance of South Korean PATRIOT missile defense batteries (against minimum energy trajectories)

However, if the missiles are launched in a lofted trajectory, PATRIOT missile defenses become ineffective. For illustration, Figure A in the online appendix shows the lofted trajectory of a North Korean missile launched from Chiha-ri, North Korea to Pusan Naval Base in South Korea. The lofted missile flies approximately 70 kilometers higher in altitude and takes 90 seconds of additional flight time. As Figure B in the online appendix demonstrates, the lofted trajectory increases the minimum required burn-out velocity to intercept the incoming missile from approximately 1.2 km/s to above 1.5 km/s. PATRIOT interceptors, however, have a maximum burn-out velocity of 1.5 km/s (see Table 5 in the online appendix). PATRIOT interceptors are unable to destroy the lofted missile heading towards Pusan Naval Base.

Similar degradation in the performance of PATRIOT interceptors is observed in five of the six modeled targets when the incoming North Korean missiles are launched on a lofted trajectory.Footnote ¹² THAAD and BMD-capable Aegis ships are necessary to provide defense against these lofted trajectories. THAAD is necessary to intercept three of the five lofted North Korean missile targeting sites in the northern and mid-latitudes of South Korea. BMD-capable Aegis ships equipped with SM-3 IB interceptors are needed to intercept the two remaining lofted missile trajectories targeting southern locations in South Korea (see Figure 2). The first experiment described above indicates the limitations of the PATRIOT terminal missile defense systems and the genuine need for other advanced missile defense assets in the region.

Figure 2 Performance of South Korean PATRIOT, THAAD, and Aegis BMD (against lofted trajectories)

In the second experiment, the list of targets is expanded to include sites in Japan and Guam (see Table 4 in the online appendix). One missile is fired at each of the thirteen targets in the region.Footnote ¹³ The target sites were chosen to encompass the most relevant military bases and command and control targets in the region. In the second experiment, it becomes clear that PATRIOT terminal missile defenses are insufficient. None of the targets in Japan can be defended using PATRIOT interceptors even when North Korean missiles travel on a minimum energy trajectory. Two BMD-capable Aegis ships are needed for regional defense (see Figure 3). The first Aegis ship expends seven interceptors and provides a defense to locations in mainland Japan (Tokyo, Yokosuka, Sasebo, Misawa, and Atsugi) and South Korea (Pusan and Chinhae Naval Bases). The second ship expends one interceptor and provides a defense to Okinawa.

Figure 3 Performance of BMD against North Korean missiles targeting South Korea, Japan, and Guam

Until this point in the experiments, it was implicitly assumed that each interceptor had a 100 percent Single Shot Kill Probability (SSKP)—that is, each interceptor will always kinematically hit its target. In most circumstances, however, the SSKP of a missile defense interceptor is less than perfect. As of April 2019, the SM-3 IA/B interceptor had registered 33 successful intercepts in 42 attempts against ballistic missile targets, approximately a 79 percent SSPK (Missile Defense Agency 2019). The THAAD missile defense system had registered 15 successful intercepts in 15 attempts, a 100 percent SSPK (Missile Defense Agency 2019). These test records, however, may not reflect actual battlefield conditions. For the analysis in this article, an SSPK of 80 percent is assumed for both the SM-3 IA/B and THAAD interceptors. Assuming that the requirement is to obtain a probability of interception of 95 percent or above for each incoming missile, Figure 4 demonstrates it would require at least two interceptors to be fired simultaneously (i.e., a barrage firing doctrine) at each of the incoming missiles.Footnote ¹⁴ Even with the doubling of the interceptors, the missile defense assets already in play can, in principle, still provide a robust defense.

Figure 4 Impact of Interceptor SSPK on Probability of Interception

In a much larger missile salvo, however, current forward-deployed missile defenses could become very stressed. For instance, in the second experiment, if instead of five targets North Korea manages to simultaneously target twelve sites in Japan with three missiles aimed at each site, it would require 72 SM-3 IA/B to defend mainland Japan.Footnote ¹⁵ Three BMD-capable Aegis ships will need to be deployed to provide the 72 interceptors needed while the fourth ship will be needed to defend Okinawa.Footnote ¹⁶ In essence, the entire available inventory of four Aegis ships will need to be used. Given that Aegis ships cannot be reloaded at sea, using all four Aegis ships during the first missile salvo could leave the US and allied troops extremely vulnerable to follow-on attacks. In the event of a follow-on second missile salvo, Japan's missile defense ships might be able to provide some defensive cover.Footnote ¹⁷

It is worthwhile to note that it is unclear if North Korea can sustain such large missile campaigns, especially against the United States, which may mount an aggressive counter-missile operation.Footnote ¹⁸ However, if North Korea does manage to do so, the present assets might be overwhelmed. As the number of available missile defense assets eventually increases, some of these difficulties can be eased. By FY2023, the number of total BMD-capable ships are projected to be 57.Footnote ¹⁹ Assuming the same ratio of ship distribution between the Pacific and Atlantic Command as presently in play, by FY2023, approximately 30 BMD-capable ships could be assigned to the Pacific Command. Such an increased inventory might be sufficient to handle any future North Korean and other regional missile threats.Footnote ²⁰

The second experiment described above shows the limitations of current missile defense deployments. It indicates how these limitations may be driving the need for a larger regional missile defense architecture in the future. The next section of the article examines the ability of various current and future missile defense deployments to dilute the Chinese strategic deterrent.

PERFORMANCE OF MISSILE DEFENSES AGAINST CHINESE STRATEGIC MISSILES

While the simulation experiments discussed earlier demonstrate the need for regional missile defenses, they still do not shed light on the accuracy of Chinese claims about the strategic impact of these defenses. A third simulation was designed to test the proposition that currently deployed US and allied missiles do not significantly alter the US–China bilateral strategic nuclear stability. The simulation results lend credence to the American argument that the US relies only on mutual deterrence against China.

China fervently objected to the US and South Korean decision to deploy THAAD. The Chinese government “demarched the US and South Korean ambassadors” and lodged formal protests against the deployment of THAAD (Meick and Salidjanova Reference Meick and Salidjanova2017, 5). A commentary in the People's Daily threatened that “if the United States and South Korea harm the strategic security interests” of China, then they will “receive a proper counter-attack” (CNBC 2016).Footnote ²¹ China also used substantial “economic coercion” to compel South Korea to reconsiders its decision (Meick and Salidjanova Reference Meick and Salidjanova2017, 3 and 7).

Chinese analysts argued that the deployment of the THAAD system and its associated AN/TPY-2 radar would enable the US to observe and track Chinese warheads and decoys, over “the entire Chinese mainland” and beyond, thereby compromising a “core national interest” (Zhun Reference Zhun2015).Footnote ²² A third simulation experiment was performed to evaluate this claim. Covering the entire Chinese mainland would require radar ranges over 4,000 kilometers. THAAD, however, is not capable of such long-range accurate tracking and discrimination. US defense officials argued that the AN/TPY-2 radar deployed in South Korea “will be configured in ‘terminal mode’ (or ‘engagement mode’) to optimize its ability to identify ballistic missile launches in North Korea and intercept them” and would not have much coverage over China (Rinehart, Hildreth, and Lawrence Reference Rinehart, Hildreth and Lawrence2015, 11 and 12). Independent studies have put the range of the THAAD radar deployed in South Korea at approximately 800 or less (Sankaran and Fearey Reference Sankaran and Fearey2017, 21–25; Lewis and Postol Reference Lewis and Postol2012).Footnote ²³ At these ranges, the THAAD radar would, in most instances, be insufficient to track Chinese strategic warheads and decoys.

As Figures 5a and 5b show, China's strategic missiles targeting the East Coast and Midwest of the United States cannot be tracked by the THAAD radar in South Korea.Footnote ²⁴ A small subset of strategic missiles targeting the West Coast of the United States is, in theory, visible to the forward-deployed AN/TPY-2 THAAD X-Band radar (see Figures 6a and 6b). China could loft these missiles over the radar or cross-target these missiles away from West Coast targets to evade detection. Additionally, current SM-3 interceptors on Aegis ships are not fast enough to engage these missiles heading towards the United States.Footnote ²⁵

Figure 5a Chinese ICBM Flightpaths to the East Coast (Washington DC) of the United States

Figure 5b Chinese ICBM Flightpaths to the Midwest (Chicago) of the United States

Figure 6a Chinese ICBM Flightpaths to the West Coast (San Francisco) of the United States

Figure 6b Close-up View: Chinese ICBM Flightpaths to the West Coast (San Francisco) of the United States

Chinese critics also posit the possibility that the increasingly larger inventory of ships could be quickly repositioned to the continental United States and might, in principle, provide a much tighter terminal defense against Chinese strategic missiles. This complaint is not without merit. The 2019 Missile Defense Review states that the SM-3 Blk IIA interceptor under development while “intended as part of the regional missile defense architecture” will also have the potential to support “existing GBIs for added protection against [rogue states’] ICBM threats to the U.S homeland.” The document further notes that “Aegis BMD-capable ships armed with the SM-3 Blk IIA interceptor will be moved into position quickly in a crisis to strengthen the defense of the homeland against rogue state missile threats” (Missile Defense Review 2019).

However, these statements in the MDR may reflect an ambitious agenda. The redeployments mentioned in the document are very difficult to successfully perform, particularly in an emergency. Gen. Vladimir Dvorkin, a frequent participant in US–Russian strategic stability talks, writes:

Additionally, assuming North Korea would possess only a small arsenal of intercontinental ballistic missile inventory in the future, it may not require repositioning a large number of ships. However, the Chinese are justified in being skeptical. In a crisis involving the US and North Korea, China would have a lot at stake and would probably find itself aligned with the North Koreans. Any substantial redeployment, even if designed exclusively with North Korea mind, may appear to China as directed towards it and forcing it to adopt escalatory postures. This indicates that as the North Korean threat evolves, it may provoke a growing tension between deploying and sustaining a strong missile defense while reassuring China on the viability of its deterrent. As discussed below, the pursuit of a combination of a reasonable increase in Chinese nuclear arsenal and negotiated reduction in the North Korean threat may be the best approach to mitigate this tension.