North Korea submarine tests 'are a critical step'
The US military is monitoring "highly unusual and unprecedented levels" of activity by North Korea's submarine force, with reports of a series of successful "ejection tests" of submarine-launched ballistic missiles described by analysts as a "critical step forward".
Three ejection tests were carried out on land at Sinpo Naval Shipyard in July, US officials told CNN. A further test was carried out at the headquarters of the Maritime Research Institute of North Korea's Academy of National Defence Science earlier in the year.
The report comes after North Korea's latest test of an intercontinental ballistic missile has shown that Pyongyang now may be able to reach most of the continental United States.
An ejection test is designed to test the cold-launch system required to propel a missile away from its launch tube on the submarine before the engine ignites, protecting the submarine.
The ground-based tests also coincide with a North Korean Romeo-class submarine carrying out "unusual activities" off the east coast of the peninsula for at least one week in late July.
The US and South Korea monitored the activities of the 1,800-ton diesel vessel. The submarine travelled more than 100km from the North Korean coast and into international waters, something which no submarine has been observed doing previously.
Analysts at the US-Korea Institute at Johns Hopkins University in Baltimore suggested there were a number of possible explanations, although the "most likely is preparations for a test in the near future of an updated Pukguksong-1 submarine-launched ballistic missile or a potentially newer system".
Pyongyang is believed to want to be able to deploy a missile-capable submarine into the Pacific Ocean as an additional threat to the United States.
"Achieving a successful cold-launch ejection test, even from land-based tubes, is a critical step forward in making an operational missile", said Lance Gatling, a defence analyst. "The whole point of putting missiles into a stealthy platform like a submarine is to achieve tactical surprise, and this moves closer to that."
The biggest problem for the North Koreans, however, is its "antiquated" and extremely noisy submarines, which make it relatively easy for US, South Korean and Japanese assets to monitor their activities, Mr Gatling said.