North Korea 'Building Massive Underground Sub Base'.

North Korea is building a massive underground facility on Mayang Island off Sinpo in South Hamgyong Province to deploy a new 3,000-ton submarine capable of carrying three to four ballistic missiles, the government here said Sunday.

Mayang Island off Sinpo in South Hamgyong Province (Picture source: Google Earth)

"We've detected recent construction of an underground facility at the submarine base," a military spokesman here said. "The project seems to improve capacity to accommodate subs and defend the base."

The shipyard in Sinpo develops and builds the subs, while Mayang Island could become the largest submarine base in the North. It seems that the North is preparing for the launch of a new sub.

The construction of the facility was detected on satellite images. Google Earth images from May showed two new 6 to 8 m wide holes on the southeast of the island, right behind a coastal artillery battery.

But information about the purpose is sparse. "The North could use the facility as a command post, shelter or storage for sub-launched ballistic missiles," the spokesman said. Or it could be a project to expand the coastal artillery battery or an anti-aircraft artillery base.

The island is believed to house some 20 to 30 subs. There are berths on the north of the island, and coastal artillery and anti-aircraft artillery batteries and an underground facility on the south side.

"The North is making it difficult for South Korean authorities to guess what type of sub it is building and whether the sub will be armed with ballistic missiles," Shin Jong-woo of the Korea Defense and Security Forum said. "That confusion could be used as a bargaining chip in its negotiations with the U.S. later.