North Korea has made significant advances over the past two decades in developing a nuclear weapons arsenal. It has detonated six nuclear devices – one with a yield of a couple hundred kilotons – and test-flown a variety of new ballistic missiles that potentially put the United States and Europe in range.

A central question about North Korea’s nuclear weapons program is whether it has managed to develop fully functioning nuclear warheads that can be delivered with a ballistic missile and, following a violent atmospheric re-entry, detonate as planned.

Agencies and officials of the US intelligence community, as well as military commanders and nongovernmental experts, are struggling to assess the characteristics and capabilities of the North Korean nuclear program.

Based on available information, we cautiously estimate that North Korea might have produced sufficient fissile material to build 30 to 60 nuclear weapons, and that it might possibly have assembled 10 to 20 warheads. It is possible that  North Korea has operational nuclear warheads for shorter-range missiles such as the Nodong. At the ranges required for intercontinental ballistic missiles, however, we have not yet seen evidence that North Korea can successfully deploy a re-entry vehicle to deliver an operational nuclear warhead.

Uncertainty about the operational status of North Korea’s nuclear warheads is not a cause for complacency, and North Korea has made considerable progress toward deploying a re-entry vehicle that can deliver an operational nuclear warhead. Achieving that goal – and thus demonstrating the capability to operate a fully functioning nuclear arsenal – is presumably only a matter of time – perhaps a year or two.

Invaluable resources for monitoring and understanding North Korea’s ballistic missile programs include the US Air Force National Air and Space Intelligence Center (NASIC), the James Martin Center for Nonproliferation Studies database on the Nuclear Threat Initiative website, The Diplomat, 38 North, and the allthingsnuclear.org blog of the Union of Concerned Scientists.¹

Land-based ballistic missiles

North Korea has a large ballistic missile force that has grown more diverse over the past decade and is expanding significantly. The force includes ballistic missiles in all major categories (see Tables 1 and 2).

Of these, North Korea’s close-range ballistic missiles, short-range ballistic missiles, and two of its three medium-range ballistic missiles are operational. One of two intermediate-range ballistic missiles might be close to operational status. One intercontinental ballistic missile (ICBM) might have a limited operational capability, while two more – and possibly four – are in development. It is important to caution that some of the ballistic missile types North Korea has flight tested might be research projects intended to develop future ballistic missile technology rather than necessarily intended for operational deployment.

Only one of North Korea’s ballistic missiles is thought to have a probable operational nuclear capability – the Nodong, a medium-range ballistic missile. But because North Korea’s nuclear warhead delivery technology is still in its infancy, current operational capability is unclear. Pyongyang’s close-range and short-range ballistic missiles, in addition to carrying conventional warheads, might have chemical warheads.

North Korea also has a number of Toksa (KN-02) close-range ballistic missiles with a maximum range of 120 kilometers. These are based on the Russian Tochka (Scarab, SS-21), which was developed as a dual-capable missile – but we are not aware of credible evidence that North Korea has developed nuclear capability for the Toksa.

Short-range ballistic missiles

Rumors circulate that some of the Scud short-range ballistic missiles may have a nuclear capability (Schilling and Kan 2015) but it is unclear if new information substantiates these rumors or if they are based on early assessments. NASIC estimates that North Korea has fewer than 100 launchers for the Scud B and Scud C short-range ballistic missiles. Many sources call the Scud-ER (Hwasong-9) a short-range ballistic missile, but (as discussed below) NASIC designates it a medium-range ballistic missile (National Air and Space Intelligence Center 2017).

Medium-range ballistic missiles

The Hwasong-9 (Scud ER) is a single-stage, liquid-fuel, road-mobile, medium-range ballistic missile launched from a four-axle transport erector launcher (TEL). The TEL is very similar to the launcher used with Scud B and Scud C short-range ballistic missiles. Many sources designate the Scud-ER a short-range ballistic missile, but in a triple test launch on September 5, 2016, the missiles apparently flew to a range of 1,000 kilometers, the lower end of the range that NASIC uses when it characterizes the Scud ER as a medium-range ballistic missile (National Air and Space Intelligence Center 2017).

The Hwasong-7 (Nodong) is a single-stage, liquid-fuel, medium-range ballistic missile carried on a five-axle road-mobile TEL. The missile, which was first test-flown in 1993, exists in two versions (Mod 1 and Mod 2) and has an estimated range of 1,200 kilometers or more. Fewer than 100 launchers are deployed. Apparently, the Nodong was originally intended to carry a first-generation nuclear warhead (Bermudez 1999), and US naval intelligence reportedly warned in 1994 that North Korea would probably be able to equip the missile with a nuclear warhead by 2000, and possibly earlier (Pinkston 2008). Some analysts believe the Nodong is the most likely missile to have an operational nuclear capability today.

The Bukkeukseong-2 (KN-15) – sometimes spelled “Pukkuksong-2” or “Pukguksong-2” – is a two-stage, solid-fuel, medium-range ballistic missile carried in a canister on a road-mobile caterpillar-type TEL. The missile, known as Polaris-2, was first test-launched in 2017, and appears to be a modification of the submarine-launched Bukkeukseong-1 (Polaris-1). It is North Korea’s first attempt to field a solid-fuel, land-based ballistic missile. The first two flight tests in 2017 demonstrated a range of up to 1,200 kilometers (Wright 2017a; Wright 2017c), which fits NASIC’s range estimate of 1,000 kilometers or more. Compared to liquid-fuel missiles, solid-fuel missiles require less logistical support and require much less preparation time before launch.

Intermediate-range ballistic missiles

The Hwasong-10 (Musudan) is a single-stage, liquid-fuel, intermediate-range ballistic missile launched from a six-axle TEL. The missile, which is also sometimes designated BM-25, has an estimated range of more than 3,000 kilometers, but it suffered several test failures in 2016. NASIC estimates that fewer than 50 Hwasong-10 launchers are deployed (National Air and Space Intelligence Center 2017).

The Hwasong-12 (KN-17) is a single-stage, liquid-fuel, intermediate-range ballistic missile carried on an eight-axle road-mobile TEL. After several failures, the missile was test-launched on a highly lofted trajectory on May 14, 2017, reportedly demonstrating that it could travel approximately 4,500 kilometers if flown on a normal trajectory (Wright 2017b). NASIC estimates the range as 3,000 kilometers or more. A subsequent test, on August 28, overflew Japan before it crashed in the western Pacific, some 2,700 kilometers from the launch site. A third successful launch on September 14 demonstrated a longer range – approximately 3,700 kilometers (Panda 2017c; Wright 2017f).

Intercontinental ballistic missiles

North Korea has developed at least three types of ballistic missiles that appear to have intercontinental range: the Taepo Dong-2, the Hwasong-13, and the Hwasong-14. Two more such missiles (or modifications) may be in development.

The Taepo Dong-2 is a three-stage, liquid-fuel, long-range missile that is thought to be a militarized version of the Unha-3 space-launch vehicle. The Unha-3 placed a satellite in an unstable orbit in 2016. NASIC estimates that the Taepo Dong-2, configured as an ICBM, could achieve a range of more than 12,000 kilometers and reach the United States. NASIC says, however, that the number of operational launchers is “undetermined.” And North Korea has not yet demonstrated a functioning re-entry vehicle for the Taepo Dong-2.

The Hwasong-13 (KN-08) is a three-stage, liquid-fuel ICBM carried on an eight-axle TEL that uses a truck similar to the one used for the Hwasong-14 ICBM. The Hwasong-13 was first displayed during a parade in 2012. At the time, some private analysts dismissed the missile as a mock-up, but unnamed officials told The New York Times that the missile had been designed with a range that made it capable of striking South Korea, Japan, and parts of Southeast Asia. And an Air Force Global Strike Command briefing in 2013 listed the KN-08 as an ICBM that “could field in [the] next [five] years” (Air Force Global Strike Command 2013).

The Hwasong-13 has not been flight tested but during a 2015 parade, a new missile that appeared similar to the Hwasong-13 – transported on the same launcher, but shorter, and with a new payload section – was initially misidentified as the KN-14, or a KN-13 Mod 2.² The 2017 NASIC report instead identified the new missile as the Hwasong-14. The new missile, with the US designation KN-20, is a two-stage, liquid-fuel ICBM carried on an eight-axle road-mobile TEL.

The Hwasong-14 was first test-launched on July 4, 2017. It flew a highly lofted trajectory, to 950 kilometers, which was assessed by experts as demonstrating a range of 6,700 to 8,000 kilometers. An unnamed US government source later told The Diplomat that the United States assessed the range to be 7,500 to 9,500 kilometers (Panda 2017a). North Korea released a video of the launch that showed the missile had a modified payload shroud – which looked similar to a shroud that appeared in photos of Kim Jung-un, engineers, and a peanut-shaped device said to be a thermonuclear warhead. North Korea claimed that the test demonstrated that it could use a re-entry vehicle to protect the missile’s warhead, but that was later shown to be inaccurate (Wright 2017d).

A second Hwasong-14 test launch, conducted on July 27, also used a high trajectory. This test demonstrated that the missile would, if flown on a normal trajectory, have a range of 10,400 kilometers. This would potentially bring western US cities from Los Angeles to Denver within striking range (Wright 2017e). The weight of the payload used in the test, which could significantly affect the range, is not known. The test did not demonstrate that North Korea has a functioning ICBM re-entry vehicle to protect a warhead.

After a two-month pause in missile flight tests, North Korea on November 29 launched its largest and longest-range missile yet: Hwasong-15 (KN-22). The two-stage, liquid-fuel missile was launched from a nine-axel TEL on a highly lofted trajectory to nearly 4,500 kilometers, which indicates a maximum range on a normal trajectory with a similar payload of approximately 13,000 kilometers, sufficient to potentially target all of the United States (Wright 2017g).

The missile carried a large and blunt re-entry body that could potentially carry a nuclear warhead. But a US official told CNN that “the North Koreans had problems with reentry” and that the payload likely broke up upon reentry into Earth's atmosphere (Starr and Sanchez 2017).

During a parade in October 2017, North Korea also displayed two new launchers with large canisters for transport of missiles. One launcher appeared similar to the eight-axle TEL used for the Hwasong-14, but modified with a large canister that resembled the missile canister used on the Russian SS-25 (Topol) TEL. The second new launcher equipped with a missile canister strongly resembled the TEL used for the Chinese DF-31A. Canister launchers are normally used to transport solid-fuel missiles, so the two new launchers might indicate that North Korea is trying to develop a solid-fuel ICBM.

Submarine-launched ballistic missiles

North Korea is developing at least one sea-launched ballistic missile, known as the Bukkeukseong-1 (other spellings used are Pukkuksong-1 or Pukguksong-1), or Polaris-1. The missile is a two-stage, solid-fuel missile designed to be carried on a single Sinpo-class submarine. The submarine only has one missile tube. The Bukkeukseong-1 was test-launched on August 24, 2016, on a lofted trajectory to range of 500 kilometers, which reportedly translates into a range of about 1,200 kilometers on a normal trajectory (Wright 2016).

Other potential platforms

No credible public information demonstrates that North Korea has developed nuclear warheads for delivery systems other than ballistic missiles – even though warheads for ballistic missiles are more difficult to develop than gravity bombs because of the extreme environment of their launch and trajectory. All other nuclear-armed states first developed nuclear bombs for aircraft and then proceeded to field warheads for missiles.

If North Korea had wanted to develop a deliverable nuclear weapon quickly, it could potentially have developed a crude gravity bomb for delivery by an H-5 (Il-28) medium-range bomber. This potential option is mentioned only for background; no public evidence suggests that North Korea has pursued it. A nuclear-capable coastal defense cruise missile, designated KN-09, was listed in the 2013 briefing by the Air Force Global Strike Command, but was deleted in a subsequent revision (Kristensen 2013).

Nuclear warheads

Assessing North Korea’s nuclear warhead capability is difficult because of significant uncertainty about the status of the nuclear warhead development program and the often contradictory – even exaggerated – information in the public domain.

After six nuclear tests – including two with moderate yields and one with a high yield – there is no longer any doubt that North Korea can build powerful nuclear explosive devices designed for different yields (see Table 3). North Korea has even published pictures of what it claims to be different warhead designs (including a “thermonuclear” design) that appear small and light enough to potentially be delivered by ballistic missiles. The published designs might be real warheads, prototypes, or models. There is no way to know for sure. Nor is it known if the published designs match the devices detonated in the nuclear explosive tests.

To better understand the status of North Korea’s nuclear weapons program, and appreciate Pyongyang’s considerable progress in developing nuclear weapons, it is useful to review major milestones and assessments from the last two decades or so.

North Korea apparently began to develop nuclear weapons even before the formal collapse of the Agreed Framework – a 1994 arrangement whereby the United States would provide Pyongyang two proliferation-resistant nuclear power reactors and North Korea would freeze operations at reactors thought to be part of a nuclear weapons program. As publicly reported in 2004, Pakistan’s Abdul Qadeer Khan said that, some time around 1999, he was shown “three plutonium devices” during a visit to an underground facility about one hour outside Pyongyang (Sanger 2004). Three years later, then–US Secretary of State Colin Powell publicly stated: “We now believe they have a couple of nuclear weapons and have had them for years” (State Department 2002).

The “weapons” Powell referred to might have been the “devices” Khan saw, or early prototype designs intended to be used in nuclear tests if necessary. But only three years after Powell’s statement, in December 2005, North Korea itself for the first time declared (Washington Post 2005) that it had “manufactured nukes for self-defense” and that the weapons “will remain [a] nuclear deterrent for self-defense under any circumstances.”

Less than a year later, on October 9, 2006, North Korea conducted its first nuclear test. The explosive yield was limited, less than one kiloton – not an impressive demonstration of a nuclear weapons capability and widely seen as a fizzle. The US intelligence community (Office of the Director of National Intelligence 2007) stated that the test produced a yield of “less than one kiloton – well below the yield of other states’ first nuclear test.”

The second test – two and a half years later, on May 25, 2009 – was a little more powerful and “suggests the North has the capability to produce nuclear weapons with a yield of roughly a couple kilotons TNT equivalent,” according to the US intelligence community.

These tests did not demonstrate the yield needed for operational nuclear weapons. A Rand Corporation report in 2012 (Schiller 2012) cautioned: “It should also be considered that even speculative sources estimate that North Korea cannot have more than a few nuclear weapons available. If they exist, these devices are very precious to the regime, and it seems unlikely that they would be mounted on inaccurate and unreliable missile systems – the risk of ‘loosing’ a weapon is simply too high.”

The third test, conducted on February 12, 2013, was more convincing. The intelligence community initially said (Office of the Director of National Intelligence 2013) that its yield was “several kilotons” – but international analysis subsequently estimated the yield to have been around 10 kilotons (NORSAR 2017). This prompted some experts to suggest that North Korea might have developed a miniaturized warhead for the Nodong – though others thought it was too soon for North Korea to have accomplished that feat (Albright 2013; Kim 2014; McGrath and Wertz 2015).

Around the same time, the Defense Intelligence Agency (Shanker, Sanger, and Schmitt 2013) – in an assessment distributed to members of Congress – for the first time concluded: “[The Defense Intelligence Agency] assesses with moderate confidence the North currently has nuclear weapons capable of delivery by ballistic missiles; however the reliability will be low.” The assessment did not reflect the conclusion of the US intelligence community as a whole and triggered an immediate rebuttal by the Defense Department: “It would be inaccurate to suggest that the North Korean regime has fully developed and tested the kinds of nuclear weapons referenced in the passage.” The Director of National Intelligence (Clapper 2013) added that “the statement read by the Member is not an Intelligence Community assessment” and that “North Korea has not yet demonstrated the full range of capabilities necessary for a nuclear-armed missile.”

Similarly, Air Force Global Strike Command (Air Force Global Strike Command 2013) stated in a briefing in September 2013 that North Korea “currently does not have an operational warhead; if developed, it could be deployed on” the Musudan (Hwasong-10), Taepo Dong-2, or Hwasong-13.³ Global Strike Command did not list any medium- or short-range missile with nuclear capability.

Even so, the assessment among private analysts at the time was that medium- and possibly short-range ballistic missiles were the first platforms for North Korean nuclear weapons. An April 2015 report (Schilling and Kan 2015) from the US-Korea Institute at the Johns Hopkins School of Advanced International Studies, for example, claimed that the Nodong missile formed “the backbone of its current deterrent… .” Similarly, after North Korea’s fifth nuclear test, in September 2016, demonstrated a yield of 10 to 15 kilotons, the Institute for Science and International Security estimated (Albright 2017) that “North Korea may have a handful of plutonium-based warheads for its Nodong ballistic missile.”

But military commanders also appeared to go further than the intelligence community at the time. The commander of US Forces Korea, General Curtis Scaparrotti, stated in October 2014: “I believe they have the capability to miniaturize a device at this point and they have the technology to potentially deliver what they say they have.” Scaparrotti cautioned that “We’ve not seen it tested,” but nonetheless added, “I don’t think as a commander we can afford the luxury of believing perhaps they haven’t gotten there.” The Pentagon press secretary (Alexander and Stewart 2014) clarified: “General Scaparrotti said he believes they have the capability to miniaturize. That’s not the same thing as saying that they have the capability to mount, test, and deliver a nuclear weapon in an ICBM.”

The South Korean Ministry of Defense did not agree with Scaparrotti’s assessment. “Despite its significant technology level, we don’t think the North is capable of making such nuclear weapons,” a spokesperson said in February 2015 (Korea Herald 2015a).

Clearly, there was confusion about how to describe the capability. On March 20, 2015, The Korea Herald (Korea Herald 2015b) quoted Admiral Cecil Haney, then the commander of US Strategic Command, about North Korea’s nuclear capability: “We think they already miniaturized some of this capability.” But when asked at a press conference only four days later if North Korea had a miniaturized warhead that it could put on a missile (Defense Department 2015a), Haney said: “As of yet, I don’t see any tests yet that [were] associated with this miniaturized claim.”

And when Adm. Bill Gortney – commander of North American Aerospace Defense Command and US Northern Command – was asked in April 2015 (Defense Department 2015b) if he thought North Korea had “developed the capability to miniaturize a nuclear warhead and put it on a ballistic missile like the KN-08,” he responded that “we assess that they have the ability to do that.”

At the time, however, North Korea had not even test-launched the KN-08, so Gortney cautioned (Defense Department 2015b): “Now, we have not seen them do that. We haven’t seen them test that.” Yet he added that “I don’t think the American people want us to – you know, there are some things that they want us to make sure we edge on the side of conservatism to make sure we get right.”

The explanation was an important reminder to be cautious when interpreting official statements about North Korean nuclear capabilities. “Our assessment,” Gortney said, “is that they have the ability to put it on – a nuclear weapon on a KN-08 and shoot it at the homeland. And that – that’s the way we – that’s the way we think. That’s our assessment of the process (emphasis added). We haven’t seen them test the KN-08 yet and we’re waiting to do that. But it doesn’t necessarily mean that they will fly before they test it.”

After its fourth nuclear test, on January 6, 2016, North Korea claimed it had successfully detonated a “hydrogen” bomb. The yield of the explosion was relatively modest (around five kilotons), and the US intelligence community assessed (Clapper 2016) the following month that “the low yield of the test is not consistent with a successful test of a thermonuclear device.” A second test that year, on September 9, was more powerful (10 to 15 kilotons), but still far from what one would expect from a successful thermonuclear test.⁴ It is possible, but unknown, that the North Korean reference to “hydrogen” implied use of tritium to boost the efficiency of a single-stage fission device. Such a technology would enable North Korea to use less fissile material in each bomb and further expand its production capacity (Jones 2016).

And it is unclear if the tests involved actual nuclear warhead designs or test devices that would require further modification to be fitted on a missile. Dennis Blair, who was director of national intelligence in 2009–2010, and is a former commander of US Pacific Command, as late as April 2017 seemed to think that the explosions involved test devices. During a talk, Blair characterized North Korea’s nuclear warheads as “these crude weapons that they developed maybe seven or eight years ago,” each of which “is about the size of half of this stage… .” Pyongyang’s program, Blair asserted (Blair 2017), “may be developing 10 to 15 nukes.”

Whether Blair was aware of later designs is not clear, but his description is a far cry from the pictures released by North Korea, whether legitimate or not, that showed the so-called “disco ball” and “peanut” warhead designs.

The 2017 NASIC report (National Air and Space Intelligence Center 2017) does not explicitly identify any of North Korea’s missiles as nuclear-capable. Nor does it state that North Korea has operational nuclear warheads. Instead, the report states: “North Korea has also tested nuclear weapons and claims its missiles are capable of carrying nuclear warheads.”

A Defense Intelligence Agency assessment leaked to The Washington Post in July 2017 concluded that North Korea had produced sufficient fissile material for up to 60 nuclear weapons and had produced miniaturized warheads that could fit inside its missiles (Warrick, Nakashima, and Fifield 2017).

Siegfried Hecker – the former Los Alamos National Laboratory director who was given unprecedented access to North Korean nuclear facilities over several years – stated in a September 2017 Bulletin of the Atomic Scientists interview (Eaves 2017) that he did not agree with the Defense Intelligence Agency’s assessment. “I don’t concur with the leaked intelligence estimate that they have up to 60 nuclear weapons now.” According to Hecker’s updated assessment (Hecker 2017), North Korea by the end of 2017 had enough bomb fuel – roughly 20 to 40 kilograms of plutonium and 250 to 500 kilograms of highly enriched uranium – to make 16 to 32 nuclear weapons, with an annual production capacity of six to seven bombs’ worth of fissile material. “If they continue to test and develop more sophisticated hydrogen bombs that could use less fissile material,” Hecker said, “we’ll have to revise that upwards.” How many nuclear weapons North Korean engineers can build with this material depends on their skill level (see Table 4).

In early August, Gen. Paul Selva – vice chairman of the Joint Chiefs of Staff – gave a detailed account of the uncertainties that remain about North Korea’s nuclear capabilities (Garamone 2017). “Before we can assert Kim Jong-un has a nuclear missile capable of targeting the United States,” Selva said, “there are a couple of aspects we must know.” He listed several criteria that must be met (Selva 2017):

• “One, [Kim] has to have the missile that will actually range that distance. We believe he has that capability right now. It’s clear that he can build a rocket that can fly that far.

• [Two,] [h]e’ll have to have the guidance and control system, the guidance and stability control, to move a rocket across that distance without it breaking up. We don’t know if he has that. We don’t know that he doesn’t. He’s been pretty successful at short- and medium-range ballistic missiles. But the physics of a long-range missile are substantially different. So stability control matters. And that’s a gap we need to fill in our understanding of whether or not he can do this.

• The third piece is a re-entry vehicle that can survive the stresses of an intercontinental ballistic missile shot. Once again, much easier to go straight up and down than it is to endure the re-entry stresses and the actual heat of an intercontinental missile shot. We don’t know if he’s got that technology. We don’t know that he doesn’t, but we don’t know that he does. He hasn’t demonstrated it. We have to see.

• And the last is a nuclear weapon that can survive that trip. Again, that’s what we don’t know. We don’t know the design specifics of his nuclear weapons – purported nuclear weapons. We don’t know if he’s been able to miniaturize it and make it stable enough.”

One month later, on September 3¸ 2017, North Korea demonstrated clearly that it could potentially produce nuclear devices with yields in the range of thermonuclear warheads. A nuclear explosion with a yield of several hundred kilotons showed that North Korea had managed to design a thermonuclear device, or one that used a mixed-fuel (composite) design. The US intelligence community reportedly (Panda 2017b) called it an “advanced nuclear device.” Yield estimates range from 140 to 250 kilotons (Asia Review 2017; NORSAR 2017).

In the public debate, Intelligence leak was seen as confirmation that North Korea had produced 60 nuclear weapons. And despite the uncertainty about the number and ability to deliver a functioning nuclear warhead to the United States, some experts asserted that North Korea could do just that.

Yet when the television program 60 Minutes asked Mark Clark, the director of the Military and Space Intelligence Center, if “Japan and South Korea and all the Americans living there are already in range of nuclear-capable missiles,” Clark responded, after a pause (Martin 2017): “They’re certainly in range of Scud- and Nodong-class missiles. Absolutely.” Apparently, they are considered to be in range of missiles, although not affirmatively in range of nuclear-capable missiles.

Apart from building the nuclear warhead itself, the key question is whether North Korea has yet developed an operationally functioning re-entry vehicle (RV) that can protect a warhead during re-entry through the Earth's atmosphere and whether the combination of the missile, RV, and warhead would function in a real attack. There is still uncertainty about this.

After the Hwasong-14 ICBM test in July, the US Central Intelligence Agency (CIA) reportedly concluded that the RV did not survive re-entry but would nonetheless likely work in an attack on the United States (Panda 2017d). Yet after the test flight of the Hwasong-15 ICBM on November 28, a US official told CNN that “the North Koreans had problems with re-entry” and that the missile likely broke up upon re-entry into Earth's atmosphere (Starr and Sanchez 2017).

The South Korean deputy minister of defense policy, Yeo Suk-joo, reportedly told the South Korean parliament that North Korea still needed to prove some technologies, like re-entry, terminal stage guidance and warhead activation (Kim and Solovyov 2017). And Seoul's Foreign Minister Kang Kyung-wha added the North Koreans “haven't demonstrated their reentry capability. They haven't demonstrated their remote targeting, or the miniaturization that is required to do this.” (Krever 2017).

Union of Concerned Scientists expert David Wright agreed that “North Korea has not not yet demonstrated a working reentry vehicle (RV) on a trajectory that its missiles would fly if used against the United States,” but added that there did not appear to be a technical barrier to building a working RV (Wright 2017h). Stanford's Sigfried Hecker estimates this might take another two years of tests (Hecker 2017).

As far as we can assess, based on the information available to us, North Korea might have produced sufficient fissile material to hypothetically build 30 to 60 nuclear weapons (if it used all the material), but only assembled perhaps 10 to 20 warheads, if even that many. If so, most of those warheads would likely be single-stage fission weapons with possible yields of 10 to 20 kilotons demonstrated in the 2013 and 2016 tests. More powerful warheads with the high yield demonstrated in the 2017 advanced design test would consume more fissile material if based on a composite warhead design or require special hydrogen fuel if based on a thermonuclear warhead design.⁵The Nodong medium-range ballistic missile appears the most likely to have some form of deliverable nuclear capability. North Korea has yet to demonstrate a capability to successfully deliver a fully functioning nuclear weapon on a long-range ballistic missile.