North Korea has long vied for nuclear-powered submarines, which would allow it to fire missiles from underwater. Advanced detection of the weapons is difficult, making the country’s construction of the warships worrisome.

Everything we know about North Korea’s nuclear-powered submarine - Photos released by Pyongyang suggest new naval vessel could carry about 10 nuclear-capable missiles

North Korea has unveiled for the first time what it says is a nuclear-powered submarine under construction, a weapons system that can pose a major security threat to South Korea and the US.