North Korea recently revealed it was building a nuclear-powered submarine for the first time. However, experts believe Pyongyang faces overwhelming technical challenges that make its nuclear submarine ambitions nearly impossible.

North Korea has conducted a slew of underwater-launched ballistic missile tests since 2016, but all launches were made from the same 2,000-tonne-class submarine which has a single launch tube. Many experts call it a test platform, rather than an operational submarine in active service.

Last week's accidental shelling of a South Korean village occurred less than 20 miles from the border of the nuclear-armed North.

The submarine could significantly escalate security concerns on the Korean peninsula and in the Taiwan Strait, experts say North Korea's construction of a nuclear-powered submarine could significantly escalate security concerns on the peninsula and in the Taiwan Strait,