Terrifying satellite images show North Korea is on track to build and deploy its first operational ballistic missile submarine.
New analysis of the November 5 pictures, obtained by Washington-based monitoring group 38 North, show a tight operation at the Sinpo South Shipyard on the country's east coast.
According to military experts, the continued movement of parts and components into and out of the port show an ongoing shipbuilding program and the construction of a new submarine, reports News.com.au.
North Korean defence and intelligence affairs expert, Joseph S. Bermudez Jr, told 38 North the pictures show an "aggressive schedule" to create the new weapon.
"A probable launch canister support, or launch canister, appears to be present within the service tower at the missile test stand suggesting the ongoing ejection testing of submarine launch ballistic missiles (SLBM)," the outlet wrote.
"Such testing could support the continued development of SLBMs, a new ballistic missile submarine or a combination of both.
"The presence of what appears to be sections of a submarine's pressure hull in the yards suggests construction of a new submarine, possibly the SINPO-C ballistic missile submarine - the follow-on to the current SINPO-class experimental ballistic missile submarine."
Analysis of the site over the past months had shown progress, but Dr Peter Layton, a visiting fellow at the Griffith Asia Institute at Griffith University, said he was surprised at how little was going on at the site.
Dr Layton believes the submarine weapon could be a back-up if the country's road mobile, nuclear-armed intercontinental ballistic missile plan fails.
However, he said the rate of building new facilities was actually quite slow.
"Given the astonishing speed of the DPRK (Democratic Republic of Korea) in building and testing new rockets the rather placid scene here is interesting," he said.
"The focus to me then seems very much on building a submarine launched ballistic missile not the submarine which will carry it.
"The DPRK might be happy with the design of the first Sinpo class and happy to build the remaining five of the class later after the missile is proven."
He also believed there was more to these photos than met the eye.
"These photos to me suggest that the DPRK submarine-launched ballistic missile (SLBM) program is more a public relations stunt intended to demonstrate DPRK technical prowess and worry others but not a war fighting weapon," Dr Layton said.
The latest analysis comes after the war of words between the North Korean Supreme Leader and US President Donald Trump reached new heights this week.
The opinion piece in the Asian country's ruling party newspaper called the United States President a "coward" for cancelling a visit to the North Korean border.
"The worst crime for which he can never be pardoned is that he dared [to] malignantly hurt the dignity of the supreme leadership," the editorial said.
"He should know that he is just a hideous criminal sentenced to death by the Korean people," it added.
The 'worst ever situation'
In the letter, North Korea described it as "the worst ever situation" because US nuclear war equipment had been deployed, ready to strike.
In a letter to UN Secretary-General Antonio Guterres, seen by Reuters, North Korean UN Ambassador Ja Song Nam said the US was "running amok for war exercises by introducing nuclear war equipment in and around the Korean Peninsula".
Three US aircraft carrier strike groups have been involved in the joint exercise in the Western Pacific in a rare show of force as Mr Trump visited Asia. The last time three US carrier strike groups exercised together in the Western Pacific was in 2007.
South Korea said the joint drill, due to finish on Tuesday, was in response to North Korean nuclear and missile provocations and to show any such developments by Pyongyang can be repelled with "overwhelming force".
However, Mr Ja said Washington was to blame for escalating tensions and accused the UN Security Council of ignoring "the nuclear war exercises of the United States who is hell bent on bringing catastrophic disaster to humanity".