Solid fueled missiles on mobile launchers on land is a logical step for DPRK to make a quantum jump in the survivability and readiness of their missile arsenal. Launch times shrink from hours to minutes — as fast as the Transporter Erector Launcher (TEL) can be rolled out of a bunker and erected.
A natural progression if DPRK is allowed to be a member of the nuclear club.
The jump to launching from a surface ship or submarine introduce another quantum jump for a more survivable platform. Submarine based platforms, in theory, can be dispersed underwater within a geography limited by their underwater endurance and greatly complicate any effort to destroy them — unless they are continuously tracked —- a resource intensive option.
Undersea endurance in turn, favors nuclear powered SSBNs that do not risk snorting.
North Korea is far away from building indigenous nuclear powered submarines compared to their ability to field a submarine launched ballistic missile.
Thus, the evidence suggest a modified Romeo or a Golf II like variant for the DPRK Sinpo-class SSB fitted with perhaps 1 S/MRBM.
Ballistic missile submarines create issues of command and control.
DPRK is not known to have developed systems like ELF for underwater communication. Wireless communication may be jammed or destroyed, leaving “Letters of Last Resort” as the only means for the Captain to make a launch decision.
At short ranges in a boomer bastion, this may not be a problem. (e.g. resort to signal flags).
What about operating areas?
The missile submarine complex at Sinpo South Shipyard is on the east coast of DPRK, bordering the Sea of Japan. The island of Mayang-Do offers the possibility of creating a mini-boomer bastion that make it a challenge to find and target the submarine by conventional ASW with our without air dominance over Sinpo.
Thus, the low endurance of a conventional submarine may not be an issue.
Later, let’s consider potential targets for a missile sub in the boomer bastion and why not base it on the west coast of DPRK.
If the DPRK nuclear missile submarine (with one missile) is to venture out, first to the Sea of Japan, and beyond, it will be targeted by one or many of (if not the) best ASW forces in the world once it is beyond the boomer bastion or coastal waters.
Making it out to ROK waters can upset THAAD’s limited angle of view, but that is still only one missile that can be countered by Aegis or other systems. Transiting past the choke points beyond the Sea of Japan with a 1970s era diesel submarine will require incredible luck, skill, and shocking incompetence on the part of allied navies guarding the exits.
For all that trouble, DPRK gets one nuclear warhead’s worth of damage.
What is the point of this when DPRK land based solid fueled mobile missiles offer just as good an option if the target is Japan, our bases in Alaska, Guam, Wake, etc.?
And they can volley launch these missiles to virtually guarantee a successful nuclear strike within 5 years.
North Korea’s submarine launched missile strategy makes no sense if the target is CONUS, Canada, or Hawaii. That is better handled with their existing liquid fueled ICBM programs that is very far along, close to maturity and ready for mass deployment.
For a surprise nuclear first strike strategy that is indicated by their ICBM basing strategy that do not need hardened silos, they got all they need.
A telltale about the DPRK submarine missile program is the apparent lack of support given by the PRC to the program. Whereas the Russians sold off Golf II submarines to DPRK for “scrap”; the PRC have sold Romeo SSKs, there has been no known major transfers of ballistic missile submarine / undersea launching technology by the PRC.
The staggering cost of operating a single SSB (even an old Golf II), would be hard to justify for either offensive or deterrent value, let alone a fleet to ensure one deterrent is always “at sea”.
Yet, we are confronted with DPRK virtually simultaneously developing both hot and cold launch systems, and apparent concern about the survivability of DPRK’s numerous short or medium range land based missiles.
Enough to warrant funding a handful (one) undersea missile submarine firing one missile?
The contrast between the lack of concern for the survivability of the ICBM force vs. the “minimal deterrent” submarine based force is stark. With only one known missile submarine based platform, it cannot provide continuous deterrent — but have to be surged out to sea “on demand” for brief periods (ranging from time below surface on battery power to fuel / food endurance).
It is, thus, consistent with a “minimal deterrent” and not offensive strategy.
The question is, deter who?
There are alternative explanations for the DPRK missile submarine strategy.
This could be the product of bureaucratic politics within the KPA: If the Army have lots of missiles, the Navy must have their own!
It could be “because they can”, or different logic, rationale, that Professor Graham T. Allison illustrated in “Essence of Decision”.
Without foreclosing on alternative explanations, one must consider what might be the North Korean rationale that can explain this prodigious deployment of resources for so little incremental warfighting capability.
North Korea’s investment in submarine based nuclear missiles is not following the model of all previous nuclear weapons powers.
The Soviets rushed into liquid fueled missiles on Hotel class diesel submarines in 1960.
The PRC until recently did not feel the need for an “at sea” deterrent.
It is not clear today that the fleet of PRC Type 094 Jin class missile submarines are fully armed with nuclear ballistic missiles and / or regularly on deterrent patrol.
Why the big rush by DPRK?
Korean empires have historically had to survive between first, the great powers of China and Japan, and then in the modern era, plus Russia and America. While the rugged terrain of Korea, particularly at the border of China and Russia provided some protection, historically, Korean rules have always had to play a delicate game of balancing off their most dangerous / threatening enemy against the others.
Thus, a persistent and repeating theme is the rapidly shifting sands of Korean alliances. When Korea is divided into multiple Kingdoms, each sought to ally with outside powers to either balance or to “unify” Korea. This pattern is very much evident today.
Koreans, culturally, traditionally, and politically, are realist to the core with mercurial loyalties.
The art of shifting alliances and allegiances, or doing whatever it takes to preserve Korea, or to unify Koreas, is deeply hard coded in the Korean DNA.
Thus, from the DPRK perspective, they must have many doubts about their historical patrons (e.g. the Soviet Union) who largely abandoned them after the fall of communism.
Likewise, there is plenty of room for doubt as to whether PRC support of DPRK will “flip”.
Can DPRK trust the Beijing-China regime to not cave to US pressure?
This brings us back to the problem of just who is the DPRK nuclear missile submarine intended to deter?
Unlike the land based ICBMs and S/MRBMs that can be both used offensively or defensively, the submarine based missile is pretty clearly a 2nd strike weapon or intended to be survivable: A minimal deterrent.
But against whom?
NORK missile submarines are unlikely to be survivable if they ventured too far. That suggest that their purpose is likely very limited. Command and control is also a major problem — when ready, the SLBM will likely have a very limited (e.g. one) targeting order to execute for their single missile. Orders can be passed by something as simple as a signal flag ashore visible on a periscope.
This suggests a target that will be extremely vulnerable, and likely not defended with any form of sophisticated defense system like AEGIS, THAAD, or even Patriots. Targets that fit this description and have a high certainty of “success” are: Beijing, Shanghai, or other major PRC cities.
No allied target fits the bill.
DPRK’s missile submarine program’s goal looks like an insurance policy to ensure that Beijing-China do not abandon them. Or to invade DPRK and knock out their land based nuclear forces.
It doesn’t make sense as a program against US and allies.
But it makes sense to ensure Beijing does not switch sides on DPRK.