Since October 2014 there have been eleven test launches of the new North Korean Pukkuksong-1 (Polaris 1) SLBM (submarine launched ballistic missile). 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 was in January 2015 was also from the bare 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 a submarine and was an ejection test that failed. Test 8 in December was publicized and showed a 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 and showed a SLBM breaking the surface (from a sub), 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 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 teste were from a submersible barge that developed by Russia and first used in the 1960s. The last three were from what appears to be a North Korea built Whale (Gorae) class sub. These last three tests were nto all successful but the latest (test 11) proved that the North Korean design was capable of doing everything an SLBM is supposed to. All these SLBM tests also indicate what while 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).
The North Korean SSB (diesel-electric submarine carrying ballistic missiles) carrying these missiles was identified in early 2015 May when aerial shipyard photos clearly (despite a camouflage net) showed an SSB under construction at the Simpo shipyard. Another North Korean missile firing sub has been spotted at sea (mostly using satellites) and it also appeared locally built but based on 1960s Russian designs and some Russian components. Another video showed this sub had one or two silos built into its sail.
This SSB turned out to be the locally built Gorae Class boat and is apparently manly used for testing the SLBM. Based on what is known so far it appears that North Korean could build more Gorae Class boats but these have limited range and endurance. They are 1,200 ton subs with one silo built into the sail. These use a lot of elderly (1960s and 70s) Russian submarine tech and require a relatively large crew of about 60 and only can stay at sea for about 30 days at a time.
North Korea obtained all or parts of a Russian R-27 SLBM in the 1990s. The R-27 is 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 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) and 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 a SLBM is tested from land facilities before it is tested from a submarine. The new North Korean SLBM is called KN-11 initially and appeared similar to the R-27 (a 14 ton, 8.9 meter long 1.5 meter in diameter, liquid fueled missile with a range of 2,400 kilometers).
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 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 Gorae SSB and the Polaris 1 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 Polaris 1 and actually detonate. North Korea says this is being worked on.