State media announced on Friday that North Korea has conducted a test of a new nuclear-capable underwater attack drone, as leader Kim Jong Un demanded an end to joint military exercises between South Korea and the United States.

According to the North Korean state news agency KCNA, the new North Korean drone conducted the test on Thursday, spending more than 59 hours submerged at a depth of 80 to 150 meters (260-500 feet). It then detonated a non-nuclear payload in the waters off its east coast.

Experts believe North Korea is demonstrating to Washington and Seoul the breadth of its nuclear arsenal, though they doubt the submarine is ready for use.

Ankit Panda, senior fellow at the American Carnegie Endowment for International Peace, stated that North Korea wants to send a message to the US and South Korea that there are many potential nuclear weapons delivery vectors that the allies would need to be concerned about and target in the event of a war.

“Silos, railcars, submarines, and mobile missile launchers on the road would all be present. And now they’re throwing in this undersea torpedo,” he continued.

The remote nation deviated from standard basing techniques on Monday by launching a short-range missile from a subterranean silo. “Haeil,” or tsunami, is the new name for drone system is intended to make sneak attacks in enemy waters and destroy naval strike groups and major operational ports by creating a large radioactive wave through an underwater explosion, the KCNA said.