Originally posted by KCNA-THE PYONGYANG TIMES:

Academy of Defence Science succeeds in test-fire of new-type SLBM

Oct. 20, Juche 110 (2021) Wednesday

The Academy of Defence Science of the DPRK test-fired a new-type submarine-launched ballistic missile on October 19.

The test-fire was directed by Yu Jin, department director of the Central Committee of the Workers’ Party of Korea, Kim Jong Sik, deputy department director of the Munitions Industry of the WPK Central Committee, and leading officials of the academy.

The academy said that it presented a report of loyalty to the Party Central Committee with pride and honour of succeeding in the test-launch of a new type of SLBM from the same ship August 24 Hero from which the first submarine-launched strategic ballistic missile was successfully launched five years ago to demonstrate the military muscle of the DPRK.

It clarified that the new-type SLBM, into which lots of advanced control guidance technologies including flank mobility and gliding skip mobility are introduced, will greatly contribute to putting the defence technology of the country on a high level and to enhancing the underwater operational capability of the navy.

THE PYONGYANG TIMES[web.archive.org]
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The Rodong Sinmun[web.archive.org]
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Originally posted by Yonhap News Agency:

October 20, 2021

The North Korean's SLBM flew around 590 kilometers at a top altitude of 60 km.

Source[en.yna.co.kr]

Whole launch sequence[web.archive.org]
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Main engine ignition[web.archive.org]
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Exhibition model[web.archive.org]
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Like all previous new solid propellant North Korean 'quasi-ballistic' missile tested in recent years, the range discrepancy of this new SLBM from Yonhap News 'informed sources' could be an indication of a similar 'pull-up manoeuvre':

• 430-450 KM [en.yna.co.kr]
  
• 590 KM[en.yna.co.kr]

In short, more difficult to detect by enemy radars, final target destination less easy to predict, while making interception by enemy missiles more challenging.