On October 2nd North Korea carried out another SLBM (submarine-launched ballistic missile) test from an east coast shipyard using a submerged barge to simulate launch from a submerged sub. The first test was in 2017. Both tests apparently used the cold launch capability of the “Polaris 1” (KN-11) SLBM (submarine-launched ballistic missile). Cold launch enables igniting the rocket motor after the missile has been ejected with a gas charge from its launch tube and into the air. This is essential for SLBMs when launched from a submerged sub. The first cold launch test occurred in 2016 and was not a success but whatever was wrong has apparently been fixed.
The Sinpo shipyard, where these tests take place, is also where a North Korean SSB (diesel-electric submarine carrying ballistic missiles) is being built. This was confirmed in early 2015 when aerial photos clearly showed, despite a camouflage net, an SSB under construction. In 2015 it was believed North Korea could have an operational SSB (carrying reliable missiles) by 2018 if they completed and successfully tested the new 2,000 ton SSB being built as well as the SLBM the sub would carry. That did not happen but satellite photos show the construction of the sub is still going on and the SLBM seemed to be working. This is not surprising because there have been a lot of tests.
Since October 2014 there have been twelve test launches of the Polaris 1. Also known as the KN-11, all tests took place off the east coast. The first two tests (one of them a failure) were from land-based silos to test the silo container and especially the ejection mechanism. Test 4 in January 2015 was also from the land-based silo and was a success. There was another such test three months later, also a success. Test 6 was in May 2015 was similar to the last previous two, was also a success. Test 7 in November was from an underwater barge and was an ejection test that failed. Test 8 in December was publicized and showed an SLBM breaking the surface (from a barge, not a sub as North Korea claimed), the engine igniting and then the missile exploded. This one was a partial success. Test 9 in April 2016 was another partial success with the SLBM breaking the surface, igniting its engine and not exploding. However, the SLBM only went 30 kilometers because of a non-explosive propulsion failure. Test 10 was in July 2016 and showed an SLBM breaking the surface from what appeared to be a sub (but was again the barge), the engine igniting and then the missile exploded when it was about 10,000 meters (32,000 feet) high. This one was a partial success. Test 11 was in August 2016 and was apparently a success. The proof was a video that showed the missile breaking the surface, the rocket engine igniting followed by rapid movement up and away. Japanese sensors detected the missiles landing about 500 kilometers from the launch site.
Many of the early tests were from a submersible barge that was developed by Russia and first used in the 1960s. The last four were from what the North Koreans claimed to be a locally built Whale (Gorae) class sub. That turned out to be untrue and all these tests were, and still are, carried out from the underwater barge using a launch silo similar to one that will be installed on the SSB. The 2016-17 tests were not all successful but since the August 2016 test, it appeared the North Korean design was capable of doing everything an SLBM is supposed to.
All these SLBM tests also indicated the North Korean SLBM was clearly based on the 1960s Russian R27 SLBM. One major difference is that the North Koreans appear to have replaced the original storable liquid fuel engine with a solid-fuel rocket motor. While the latter requires less maintenance onboard and is more reliable, it has half the range (about a thousand kilometers) compared to the R27 (over 2,000 kilometers). South Korean intel analysts point out that the current KN-11 design could accommodate a solid-fuel rocket motor capable of extending the range to over 2,000 kilometers. This would make KN-11s with nuclear warheads a threat if the North Korea SSB became operational. Such a diesel-electric sub could travel to a position off the American West Coast and hit a lot of valuable targets west of the Mississippi River.
There appear to be two North Korean SSBs. The first one is smaller and locally built. This SSB is apparently meant for testing the SLBM. That may have been the intention but apparently the first of several “Sinpo Class” SSBs were part of an ongoing effort to come up with an SSB design that could actually carry and launch two or three KN-11 missiles from somewhere close to North America, Based on what is known so far it appears that North Korea may have moved from the first 1,200 ton Gorae/Sinpo Class design to a larger (over 2,000 tons) SSB design that could make it across the Pacific. Sinpo 1 design had limited range and endurance. It was a 1,200 ton sub with one silo built into the sail. Sinpo 1 used a lot of elderly (1960s and 70s) Russian submarine tech and required a relatively large crew of about 60 and could only stay at sea for about 30 days at a time. This design was also noisy and easy to detect. There may or may not be a larger Sinpo 2 or Sinpo 3 sub under construction but there is not conclusive proof. Until a larger, reliable and quieter SSB is available the KN-11 SLBM is of little use.
What North Korea went through to develop the KN-11 shows how difficult the process was. Initially, North Korea obtained all or parts of a Russian R-27 SLBM in the 1990s. The R-27 is a 1960s vintage tech that was replaced in the 1970s by more modern designs. But many of the unused R-27s produced were recycled for scientific research launches until 1990. Some 500 R-27s had been launched with an 87 percent success rate. It was believed that all or much of at least one missile was illegally sold as “scrap” to North Korea in the 1990s. This was deduced from the fact that after the Soviet Union collapsed in 1991 North Korea bought a lot of discarded Russian weapons for scrap, none of which was supposed to be operational stuff. It was later discovered that some of the scrap was remilitarized by the North Koreans. Thus it was no surprise that the new North Korean Musudan ballistic missile looked a lot like the R-27. There are pictures of the Musudan mounted on a large truck (that serves as transport and launcher) not a submarine. So far there has been no evidence of a Musudan test. Typically an SLBM is tested from land facilities before it is tested from a submarine.
Developing an SSB took a similar route. North Korea also received ten decommissioned Russian Golf class SSB in 1993, to be turned into scrap. The Golf class boats used the 16 ton R-21 SLBM, which is thinner and longer than the R-27 that replaced it, in the first Russian nuclear powered SSBNs, in the 1960s and 1970s. Foreign intelligence agencies have been watching North Korea carefully for signs that North Korea was working on an SSB but the only possibility found was one new submarine under construction. It did not look like a copy of the Golf class boats but did have a sail that might have held an R-27/Musudan type SLBM. In any event, this boat seemed to be under construction for a long time and largely hidden from view. The scrapped Golf boats enabled the North Koreans to examine the first generation SLBM launch equipment, in which SSBs fired missiles from an elongated sail structure that contained three SLBMs. The eventual appearance of the Simpo class SSB and the KN-11 SLBM is another example of North Korea adapting decades old weapons so they could be built in North Korea. The only missing piece is a nuclear warhead small and rugged enough to fit into the KN-11 and actually detonate. North Korea says this is being worked on. Less is said about the SSB effort, which indicates, based on past North Korean performance, that there is a lot more to be done to produce a sub that could carry and launch KN-11s at targets in the western United States.
This does not seem to bother the North Koreans because the SSB/SLBM delivery system is seen as a backup for the preferred ICBM approach. While the SSB can be more easily tracked and destroyed before it gets within the launch range of North America, the U.S. already has anti-missile systems in place to intercept a small number of North Korean ICBMs. The SSB could get past those anti-missile systems and launch close to the North American coast. In any event, the North Korea nuclear weapons continue to have a hard time acquiring the ability to attack the United States.