As 80,000 U.S. and South Korean troops practice fighting a North Korean invasion during military exercises this month, the North successfully launched a submarine-based ballistic missile that regional leaders call a "grave threat to security."
The launch of a "Pukguksong" KN-11 missile took place on August 24, with South Korean government estimates indicating the missile could be ready to deploy aboard North Korean subs as early as next year.
The KN-11's range is unknown.
The North's submarine was just off of Sinpo, on the east coast of the country. It flew 500 kilometers (roughly 310 miles) before falling into the Sea of Japan. The South Korean military believes it could strike twice as far.
North Korean leader Kim Jong Un said the test-firing proved the DPRK "joined the front rack of the military powers fully equipped with nuclear attack capability," and "the U.S. mainland and military bases in the Asia Pacific are now within the striking range of the DPRK's military," according to the North's official news service..
Related: New study says North Korea uses war games as an excuse to be difficult
The missile fell inside Japan's Air Defense Identification Zone. Japanese Prime Minister Shinzo Abe called the launch a "grave threat to security" and lodged a strong diplomatic protest.
It was the North's "greatest success and victory," Kim said in a statement.
The North previously tested a missile on July 8, the day after South Korea and the United States announced the deployment of Terminal High Altitude Area Defense missile systems in the South.
The missile gives North Korea a "second strike" capability, meaning the north could launch a retaliation of the U.S. and South Korea preemptively destroyed its land-based nuclear sites.
North Korean submarines are electric powered and must surface to recharge their batteries. This limits their range, preventing the subs from maneuvering undetected within launching distance of the American west coast.