STORY: North Korea says it has successfully tested a nuclear-capable undersea attack drone, designed to create massive radioactive waves when detonated below the surface, hitting fleets of enemy ships or coastal areas.It's dubbed the "Haeil," or tsunami in Korean. These images from North Korea's state-run media show leader Kim Jong Un standing next to a large torpedo-like object, which it didn't identify, and the object exploding underwater. But how capable could such a weapon be?Kim Dong Yub is with the University of North Korean Studies in Seoul, South Korea."The distance makes it capable of attacking almost any port in South Korea where the U.S. army is located even if it is launched from any port in North Korea. But it’s not just that. The North said it could be carried by ships. If it’s carried by a ship camouflaged as a merchant ship, it can hit Japan’s Yokosuka port, where the U.S. army is at or even further, like Guam, which is very worrisome.”“It’s conventional, but it’s very hard to detect. Also, it is highly likely not to make big noises. North Korea had planned this 11 years ago and conducted secret tests for about 50 times over two years.""I would say the weapon system should be pretty solid.”North Korea made the announcement as South Korea and the U.S. conducted joint military drills in the region.The North says it did not use a nuclear payload in the drone test and a U.S. official, speaking anonymously to Reuters, said there was no indication of one.It's not clear if North Korea has fully developed the kind of miniaturized nuclear warhead needed to fit its smaller weapons.Regardless, the Carnegie Endowment for International Peace, the Washington D.C. think tank, has said the concept of the Haeil is similar to Russia's Poseidon nuclear torpedo, which both American and Russian officials have described as an emerging class of weapon that can render coastal cities uninhabitable.And, according to the think tank, the Haeil demonstrates that Pyongyang wants to show off an increasingly diverse range of nuclear threats to its enemies.A South Korean military official said they were analyzing the North's claims.