N.Korea Conducted Tests of Sub-Launched Missiles

North Korea conducted an ejection test of a missile's "cold-launch system" at a naval shipyard in Sinpo, South Hamgyong Province on Sunday, CNN quoted a U.S. defense official as saying Monday.

It was fourth such test this year and the third in July alone.

"The U.S. military has detected 'highly unusual and unprecedented levels' of North Korean submarine activity and evidence of an 'ejection test,'" CNN added.

The "cold-launch system" uses high-pressure steam to propel a missile out of the launch canister into the air and let the engine ignite. It aims to prevent the heat from the engine from damaging the submarine or submersible barge that launches the missile.

If the North succeeds in developing both land-based and submarine-based ballistic missiles, it would have two-thirds of what has been described as a "strategic triad" of land, air and sea-based nuclear attack capabilities.

The regime recently sent a diesel-powered Romeo-class sub about 100 km out to sea in international waters from the East Sea and outfitted a Sinpo-class sub with a possible missile launch tube, U.S. defense officials told CNN.