That article is by Sean Gallagher at arstechnica published May 12, 2015 concerning North Korea's alleged submarine launch of a ballistic missile. The submarine and missile details will need to be fully verified by intelligence agencies before they are taken as fact.
On May 13, 2015, US intelligence said North Korea (NK) may have achieved what is called a limited compressed gas ejection test. This is called a perhaps 200 meter "cold launch" in the vertical launch business.
Other US theories that the missile test did not happen in the way NK said or did not happen at all, are:
- NK launched the missile from a barge-sea platform, not a submarine, and/or
- the missile was a non-working dummy capable of cold launch but nothing else, and/or
- NK photoshopped the missile images below, making up the whole "event".
Despite these doubts South Korea is more than usually concerned. NK has proven it can conduct real nuclear tests and has tested ballistic missiles with, at least, proven medium ranges (ie. between 1,000 km and 3,000 km). Now NK is working towards an SLBM capability. Hence South Korea (and the US) are exploring strategies and tactics to react to NK SLBMs. See my April 16, 2015 article which mentions a future South Korea "Kill Chain" pre-emptive strike capability.
The arstechnica string is http://arstechnica.com/tech-policy/2015/05/north-korea-test-launches-polaris-1-ballistic-missile-from-submarine/ :
"North Korea test-launches “Polaris-1” ballistic missile from submarine