Why is North Korea growing its navy with submarines and nuclear drones?

Over the past year North Korea has moved to boost its navy with new nuclear weapons, including an underwater drone, warships, and its first operational missile submarine, unveiled on Friday.

North Korea's navy has historically been dwarfed by the country's land forces, and overshadowed by its rapidly advancing ballistic missile program.

Now, leader Kim Jong Un has said the navy will play a key role in the country's nuclear deterrence, and analysts say it may also assure support among naval commanders and boost national pride.