Tracking North Korean SSBN’s: Why Diesel Boats Won’t Cut It
North Korea’s SSBN program has made South Korean SSN acquisition a requirement, not an option
This article is part of an ongoing series examining South Korea’s nuclear submarine program, a once-controversial initiative that has evolved into one of East Asia’s most consequential naval procurement decisions. Each installment explores different dimensions of this strategic shift, from legal frameworks and political dynamics to regional implications and technological challenges. Read the complete series here.
The New York Times recently quoted a former South Korean government official who opposed his country’s nuclear attack submarine (SSN) program. He opined, “Which is more efficient in patrolling the crowded streets of Seoul: 10 Hyundai Sonata cars or one Mercedes-Maybach?”
He is arguing that SSN’s are expensive luxury items whose mission could be undertaken by lower cost diesel boats. While it’s a catchy soundbite, it’s dangerously misleading, as diesel boats simply cannot reliably conduct the South Korean SSN’s single most important mission which will be to continuously track North Korea’s nuclear ballistic missile submarines (SSBN).
Not All Submarines Are Created Equal
The question of whether South Korea should acquire SSN’s has been hotly debated for years. Proponents have often cited benefits associated with faster speed, longer duration, and wider combat radius. While such benefits may enhance the country’s naval power, SSN cost-effectiveness came into question.
Also, the Republic of Korea Navy (ROKN) already possesses a top-notch submarine force comprised of highly trained submariners who operate the KSS-2 (Type 214) and KSS-3 boats which are both reputed to be among the world’s quietest and stealthiest.
In March 2023, the framework of this debate changed dramatically when North Korea revealed its intention to build SSBN’s. Once these SSBN’s become operational, continuously tracking them will become one of South Korea’s highest national security priorities, as SSBN’s represent mobile, survivable nuclear launch platforms that can threaten the existence of South Korea, Japan, and beyond.
While conventional submarines can be used for limited tracking (i.e. several hours) of SSBN’s, continuous tracking (i.e. 1+ days) with a conventionally powered submarine is simply not possible. Here’s why:
Endurance Mismatch: While the ROKN’s diesel boats can stay submerged for up to three to four weeks, SSBN’s can remain underwater for months. In any shadowing operation, the SSBN can simply outlast the diesel boat and break contact. Once that happens, relocating a submerged SSBN becomes extraordinarily difficult.
Speed Limitations: Diesel boats are much slower than SSBN’s, which can sustain 30+ knots for extended periods. If an SSBN decides to sprint, a diesel boat cannot maintain contact. This speed differential is fatal for persistent tracking.
Detection While Snorkeling: Diesel boats must eventually snorkel to recharge batteries or run diesel generators. This creates acoustic signatures and exposes periscopes or masts that can be detected. SSBN’s never face this vulnerability, as they can remain submerged for far longer.
No Historical Precedent: No navy has ever successfully deployed diesel boats to shadow SSBN’s on a routine operational basis. There’s a reason: the mission requirements exceed what diesel propulsion can physically deliver.
Simply put, while diesel boats can be used to track SSBN’s for a few hours, continuous shadowing with diesel boats is not an experiment any responsible defense planner should want to run.
Aside from diesel boats, some SSN opponents have mentioned uncrewed underwater vehicles (UUV) as a potential alternative, as UUV’s are expected to replace crewed submarines in certain types of operations. However, SSBN tracking isn’t expected to be one of them, and it appears that will be the case for the foreseeable future due to technical limitations, such as those related to power supply, communications, and stealth.
The crewed SSN requirement for SSBN tracking remains fundamentally the same as it was during the Cold War. Despite decades of progress in autonomous systems, UUV’s cannot yet reliably shadow SSBN’s over extended periods in contested environments.
Why Not Just Rely on the USN?
Offloading this responsibility to the USN might sound like a reasonable option, but it probably won’t be palatable in both Washington and Seoul.
The USN faces resource constraints across the board, and American SSN’s will be prioritizing a very large and growing Chinese submarine force capable of threatening the USN throughout the Indo-Pacific theater. On top of this, the USN has commitments in other parts of the world. Dedicating SSN’s to continuously shadow North Korean SSBN’s means pulling them from other critical missions. This situation is exacerbated by the ongoing shortage of American SSN’s and insufficient industrial capacity to support their timely construction.
That said, let’s say hypothetically that the USN could handle tracking North Korean SSBN’s. Outsourcing this critical mission to another country may not sit well within South Korea. Tracking and countering North Korean SSBN’s is about national survival. The government in Seoul needs to maintain awareness of these SSBN’s at all times and will most likely want to own the intelligence about these boats.
The Bottom Line
For decades, South Korean nuclear submarines were debated as optional enhancements. North Korea’s SSBN program should end that debate. When diesel boats physically cannot track SSBN’s over prolonged periods, nuclear submarines become a requirement, not a choice. South Korea needs sovereign capability to track nuclear weapons platforms threatening its existence. This is about national survival, and opponents need to understand that reality.