Pyongyang is naturally secretive about its submarine-launched ballistic missile program and has carefully guarded the details of it. Because of this, post-test estimates of the program’s progress have varied. An anonymous South Korean defense official told the media that North Korea could develop a fully operational system within two to three years. U.S. officials, however, believe a fully functional system is far from completion and allege the test was not actually carried out from a submarine. Instead, they suggest it was a simulated firing to test an underwater ejection system, perhaps from a towed launch pad.
Fielding a submarine-launched ballistic missile is difficult. The technology is much more complex than land-based missile technology, which itself has already proved challenging for North Korea. Underwater launch first requires a successful ejection system and a gas generator for reducing hydrodynamic resistance. Still, a reliable submarine-launched ballistic missile is not completely out of North Korea’s reach. With time, continuous tests and the necessary resources, the North Koreans could eventually develop a successful system.
The technology for the missile system itself, however, is just one aspect of a successful system. A sea-based nuclear missile capability hinges on developing an adequate carrier vessel — a ballistic missile submarine. Without a large, stealthy and long-range submarine, the North Korean submarine-launched ballistic missile effort will simply consume significant resources without altering the nuclear equation.
On paper, North Korea’s submarine fleet is quite large, comprising around 70 vessels. But the majority of these are mini-submarines that displace about 300 tons of water and are unsuited for operations beyond littoral waters. The North Korean navy’s largest submarines at the moment are Chinese Type 033 vessels. These are copies of Russia’s 1950s-era Romeo-class submarines and displace 1,830 tons. Rumors suggest North Korea is developing a replacement for these submarines: the Sinpo-class. These new vessels, however, are unlikely to exceed the capabilities of the improved Type 033 variants currently in use and will be of around the same size, displacing approximately 1,500 tons.
Unfortunately for Pyongyang, the Sinpo-class submarines under development simply do not meet the requirements to be an adequate ballistic missile launching platform. In order to function in this capacity, a submarine would need to be of sufficient size to carry a ballistic missile. The smallest submarine to ever carry a submarine-launched ballistic missile is the Soviet Zulu IV-class, which carried one to two nuclear ballistic missiles, displaced approximately 2,000 tons and was a full quarter heavier than North Korea’s Chinese Type 033 or Sinpo-class submarines. Pyongyang will need bigger vessels in the future to carry one to two missiles in an operational capacity. To carry more would require a new and entirely different class of submarine.
Despite these challenges, the benefits of a fielded submarine-launched ballistic missile are substantial. This capability would give North Korea two advantages not offered by ground-based missiles. First, it would extend the reach of North Korea's missile systems and theoretically enable it to strike targets outside of ground-based missile range. Second, submarine-launched missiles, because they are offshore and mobile, would give North Korea a second-strike capability, allowing it to retaliate against attacks on its land-based nuclear bases and launch pads. These benefits assume, however, that North Korea’s submarines have an adequate level of endurance, the amount of time a vessel can remain at sea unsupported. Submarines would need to be able to remain unsupported long enough to reach targets beyond the range of land-based missiles. In order to fulfill a second-strike role, vessels would need to be deployed for months far from vulnerable ports and remain ready for counterattack.
North Korea’s current Type 033 submarines, even with modifications, cannot meet these endurance requirements. A fully functioning KN-11 missile would have a range of approximately 2,500 kilometers (1,553 miles). The Type 033 submarine has a range of around 15,000 kilometers. This is not enough to approach within 2,500 kilometers of the U.S. mainland and return without at-sea refueling. Were North Korea to refuel these vessels at sea, it would significantly degrade the stealth variable of these vessels.
Stealth would be essential in order to avoid being detected and neutralized by an enemy in long patrols at sea or a mission to the U.S. mainland. The Type 033 is a diesel electric boat and can be stealthy in short missions within littoral waters. Beyond these near-shore environments, however, the submarine would have a more difficult time concealing itself without the noise or clutter typically found in littoral waters. The Type 033 would also be forced to spend significant time at the surface to recharge its batteries by running its diesel engines, a process for which they need atmospheric oxygen. Many of the latest conventional submarines, by contrast, are equipped with air-independent propulsion, which means they do not need to surface to run their engines.
Without an adequate submarine, the resources Pyongyang is investing in new missile technology will not improve the capability of its existing land-based missile program. The missiles in the current KN-08 program will still have greater range and will be able to be more rapidly dispersed in large numbers and in difficult terrain. Eventually, North Korea could develop a suitable ballistic missile submarine, but it would take several years to complete. Such a development would truly change the nuclear equation. For now, however, the successful test conducted May 9 is not going to alter North Korea’s nuclear capability.