On May 9, a Korean People's Army Naval Force submarine test-launched a ballistic missile off the eastern coast of North Korea. The test launch, reported by North Korea's Rodong Sinmun newspaper, only traveled about 150 meters, according to South Korean defense officials. But it demonstrated that North Korea had developed the capability of performing submerged launches of missiles well ahead of previous intelligence estimates. Based on the launch, South Korean officials now believe that North Korea could have a limited submarine-launched missile capability deployed to its fleet of submarines within the next five years.

The test comes as South Korea nears a decision on the deployment of a Terminal High Altitude Area Defense (THAAD) anti-ballistic missile system. China has been pressuring South Korea to not allow the deployment, but an earlier, barge-based test of the submarine-launchable missile (named "Polaris-1" by North Korea) on April 22 has made the deployment more likely.

Polaris-1 is apparently a close copy of a Soviet-era R-27 submarine-launched ballistic missile (SLBM), a liquid-fuel missile which had the NATO designation SS-N-6 "Serb." This is the third test launch of the missile this year, but it is the first submarine launch. Developed in apparent violation of a UN resolution banning North Korean ballistic missile development, the missile could have a range of about 1,500 miles.

The original R-27 was capable of carrying three independent nuclear warheads. An explosion of an R-27 missile caused by a reaction between a seawater leak and fuel residue aboard the Soviet "Yankee" class ballistic missile sub K-219 in 1986 off of Bermuda led to one of the most tense moments in the late Cold War (later breathlessly and inaccurately recounted in one of the worst submarine movies ever, Hostile Waters).

North Korean leader Kim Jong-un, who had previously planned to travel to Russia over the weekend but then cancelled his plans last week, was on hand to observe the launch. "He stressed that the acquisition of the technology of firing ballistic missile from a strategic submarine underwater made it possible for the KPA to possess a world-level strategic weapon capable of striking and wiping out in any waters the hostile forces infringing upon the sovereignty and dignity of Songun Korea and conduct any underwater operation," reported the Korean Central News Agency, North Korea's government news service.

Almost all of North Korea's existing submarine fleet is made up of diesel-electric submarines with limited range, including about 20 based on the 1950s Soviet Project 633 ("Romeo") design imported from China or locally built. A new submarine with one or two vertical missile launch tubes in its sail was spotted being built at North Korea's Sinpo South Shipyard last summer. North Korea also obtained 10 Soviet Golf-II diesel-electric ballistic missile submarines, built in the late 1950s, from Russia in 1994. The Golf-II, or "Project 629A," submarines, which are capable of carrying three SLBMs, were transferred by Russia as scrap to North Korea. However, it is now believed that North Korea has been working on reactivating some of the subs and that one was used for the test launch this weekend.

The Golf-II class carried the R-27 missile toward the end of its active duty in the Soviet Navy and had an operational range of 9,500 nautical miles (about 11,000 miles). They were capable of 17 knots (about 20 mph) when running on the surface and 12 knots (about 14 mph) when submerged. So in theory, a North Korean Golf-II submarine could get in range of the United States for a launch, but it would require being at sea for two to three months to get close enough to strike, transiting a lot of open ocean. The Korean Peoples' Army Navy is mostly a coastal force with no deep-water experience, and diesel subs transiting the Pacific would be easy targets for US sensors and patrols.

The bigger concern is that these subs could evade detection in Korean coastal waters and launch attacks against South Korea and Japan with little warning. Jeffrey Lewis of the California-based Monterey Institute of International Studies told Reuters, "While North Korea's submarines are not especially effective, the challenge of finding even a small number of specific submarines armed with missiles would be quite a challenge."