• North Korea unveiled a new "tactical" missile submarine in September.
  • The sub appears designed to carry a mix of ballistic and cruise missiles.
  • That mix may reflect desire for more firepower — or an inability carry the North's largest SLBMs.

In September, North Korea launched the Hero Kim Kun Ok, a diesel-electric-powered ballistic missile submarine.

Officially known as Tactical Nuclear Attack Submarine No. 841, the sub is a radically redesigned variant of a 1950s-era Soviet Romeo-class attack submarine equipped with 10 launch tubes — four for submarine-launched ballistic missiles and six for submarine-launched cruise missiles.

SLCMs, as they're known, fly at lower altitudes and are usually armed with conventional warheads for strikes on smaller targets on or near the battlefield. SLBMs are designed to carry large payloads, sometimes multiple nuclear warheads, and strike bigger, more distant targets, like cities, at higher speeds, often exiting and reentering the atmosphere during flight.

The mixed arsenal on North Korea's new sub, as well as Pyongyang's designation of it as a "tactical" rather than "strategic" vessel, surprised most observers, who expected the sub, which has been under construction since at least 2019, to be outfitted to launch North Korea's largest SLBMs.

North Korea's mixing of SLBMs and SLCMs on the new sub may be out of desire for more firepower. It could also be something more embarrassing: North Korea's large "strategic" SLBMs may just be too big to fit in the submarine launchers it can build.

Indeed, only one model of SLBM, which appears to be a naval variant of a smaller "tactical" short-range ballistic missile, is believed to fit in the launchers aboard the Hero Kim Kun Ok.

North Korean SLBMs

North Korea Kim Jong Un submarine
Kim Jong Un at the launch of a new "tactical nuclear attack submarine" in early September.
KCNA via REUTERS

North Korea has a clear reason for pursuing missile-launching submarines and SLBMs. The overwhelming superiority of US and South Korean air, naval, and land forces could directly threaten the Kim regime's survival in a war.

Indeed, a key pillar of South Korea's military strategy to counter the North's missile and nuclear forces is the ability to launch pre-emptive precision strikes against them.

Consequently, North Korea is trying to diversify its launch methods to make it harder for South Korea and its allies to find those weapons on the ground. Pyongyang has deployed missiles on mobile launchers, in train cars, and aboard submarines.

Subs in particular provide a good platform to hide nuclear-armed missiles and launch pre-emptive or retaliatory strikes whenever necessary.

But there are doubts that North Korea's submarines can operate effectively enough to carry out that mission, and while Pyongyang's progress on sub-launched missiles has worried its neighbors, its mixed testing record suggests that those subs may not have much to carry into battle anyway.

Pukguksong and company

north korea submarine missile launch water kcna reuters
A sub-launched ballistic missile is test-fired in a photo released by North Korea in April 2016.
KCNA/File Photo via Reuters

North Korea has built and tested three models of SLBMs since it began developing those missiles roughly two decades ago. It began ejection tests with its first SLBM, the Pukguksong-1, in 2014. ("Pukguksong" translates to "Polaris" and may be jab at the American SLBM of the same name.)

That same year, North Korea's first ballistic-missile sub — which is widely seen as a platform meant for testing SLBMs — was spotted by satellites. It was unveiled to the public in 2015, when Pyongyang released images of a supposedly successful launch test.

Externally similar to the Soviet R-27, the Pukguksong-1 is a two-stage solid-fueled SLBM. It has undergone multiple tests, including at least five flight tests, the first in November 2015.

The first four tests were either complete or partial failures, but the fifth, in August 2016, was a total success, with the missile launching from a sub and flying 310 miles before landing in the Sea of Japan. It is the only successful test of the missile so far, and led to estimates that the missile's range is roughly 745.65 miles.

After developing the Pukguksong-2, a land-based variant, North Korea produced the Pukguksong-3, another two-stage solid-fueled SLBM. The Pukguksong-3's existence was first suggested by diagrams seen in the background when Kim visited a facility that builds missile engines in August 2017.

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Photos of a new sub-launched ballistic missile during a test in October 2021.
KCNA via REUTERS

The Pukguksong-3's only known test was in October 2019. It flew 279 miles and reached an apogee of 564 miles, leading analysts to estimate its range at 1,180 miles, which would allow it to reach all of South Korea and most of Japan.

North Korea proved it was capable of launching an SLBM from a submarine in October 2021 — just weeks after South Korea launched its own SLBM for the first time — when its first ballistic-missile sub successfully launched a new SLBM. (Previous North Korean SLBM tests had occasionally used a submersible test barge.)

During the 2021 test, the missile, which Pyongyang has not named, flew about 372 miles and reached an altitude of 31 miles. The unnamed missile differs significantly from the Pukguksongs, as it appears to be a naval variant of the KN-23 short-range ballistic missile, which is likely a North Korean copy of Russia's Iskander-M.

The navalized KN-23 was tested twice more — in May and September 2022 — and achieved similar ranges both times, though in the September test it was launched from a silo or a platform submerged in a reservoir. The missile is believed to have a shorter range than its named predecessors and is therefore seen as a "tactical" missile rather than a "strategic" SLBM.

New models, same targets

North Korea navy Pukguksong submarine-launched ballistic missile
A Pukguksong sub-launched ballistic missile in a military parade in Pyongyang in April 2017.
REUTERS/Damir Sagolj

North Korea has shown off three more SLBM models at parades. The Pukguksong-4 was displayed in October 2020 and the Pukguksong-5 in January 2021. A third SLBM strongly resembling the Pukguksong-3, -4, and -5 was seen in an April 2022 parade, but like the navalized KN-23, it had no markings and has not been officially named.

Those missiles all appeared to be larger than the Pukguksong-3. As impressive as they look, however, the fact that North Korea hasn't tested any of them — or done additional testing of the Pukguksong-3, for that matter — suggests it does not yet have the capability to mass produce and field strategic SLBMs.

Pyongyang has tested multiple types of new missiles, including hypersonic missiles, since the last Pukguksong-3 test, so the lack of further SLBM testing may mean that the SLBM program is a lower priority than newer ground-based missile programs.

Moreover, none of the new SLBMs, and possibly not even the Pukguksong-3, are believed to be able to even fit inside the Hero Kim Kun Ok, the sub launched in September. Instead, that sub is believed to be armed with four navalized KN-23s and six SLCMs — a far cry from predictions that it would carry at least three Pukguksong-3 SLBMs.

North Korea submarine
North Korea's new "tactical nuclear attack submarine" at its launch in early September.
KCNA via REUTERS

The armament explains why Kim labeled the Hero Kim Kun Ok a "tactical nuclear attack submarine." As North Korea can't reliably build and deploy strategic SLBMs, it is loading the sub with tactical nuclear weapons instead.

Large SLBMs are tough to build and operate, but North Korea is "likely still keeping to the goal of longer-range sea-based missiles," Ankit Panda, an expert on nuclear weapons and missile defense at the Carnegie Endowment for International Peace, told Business Insider.

"That said, given the limitations on stealth and mobility when it comes to the North Korean submarine fleet, the navalized KN23 provides many of the same benefits strategically as a somewhat longer-range SLBM," Panda said.

Using smaller "tactical" nuclear weapons would, of course, still have strategic effects in any conflict, but for now the threat from Pyongyang's SLBMs appears limited to the targets they can reach in South Korea and in parts of Japan.

Kim has declared that North Korea will expand its fleet of diesel-electric ballistic-missile submarines by converting all its remaining Romeo-class boats to at least the Kim Kun Ok standard. Kim also declared that North Korea will build its own nuclear-powered subs to further "the nuclear weaponization" of its navy.

Pyongyang may have limited ability to realize those ambitions, but its pursuit of them may well make SLBMs a higher priority in the years ahead.