“If the North decides to pursue such a capability, it is likely to take years to design, develop, manufacture, and deploy an operational submarine-launched ballistic missile force,” Joseph S. Bermudez Jr., chief analytical officer at AllSource Analysis, wrote last week on 38 North, a blog run by the U.S.- Korea Institute at Johns Hopkins School of Advanced International Studies in Washington.

A North Korean submarine with working missile silos would mark a giant stride in Kim’s ability to threaten distant rivals, including the U.S., as his regime claims it can now make warheads small enough to be deployed on missiles.

The U.S. and South Korea remain vigilant on North Korean submarines among an array of threats the country poses, Kwon Ki Hyun, a spokesman for Seoul’s Defense Ministry, said today by phone. He declined to confirm a Yonhap News report yesterday that the North modified a Soviet-era diesel submarine to build its own vessel that could eventually be capable of firing ballistic missiles. Yonhap cited an unidentified South Korean government official.

Nuclear Tests

North Korea, which has conducted three nuclear tests since 2006, has been trying to modify Soviet-era submarines so they can be used to launch SSN6 missiles, South Korean Defense Ministry spokesman Kim Min Seok said in September. He said then that the North hadn’t yet succeeded in making its subs capable of firing missiles.

“The North Koreans are poor, but not stupid, and they do have some pretty good engineers, especially in weapons areas,” Dean Cheng, who specializes in military capabilities as a research fellow at the Heritage Foundation in Washington, said in an e-mail. “But modifying a submarine is no mean feat, and would take a lot of time and be risky, especially as it would require compromising the hull’s integrity and would likely make a fairly noisy boat even noisier.”

North Korea has built a test pad in its eastern coastal city of Sinpo that is “probably intended to explore the possibility of launching ballistic missiles from submarines or of a shipboard vertical launch ballistic missile capability,” Bermudez wrote, citing commercial DigitalGlobe images from July.

Warship Torpedoed

North Korea has 1.2 million troops and operates about 70 submarines, while the South has 10 of the vessels, according to a 2012 South Korean defense white paper. South Korea accused the North of torpedoing one of its warships in 2010, resulting in the deaths of 46 sailors, a charge the North denies.

In June, North Korea released photos of Kim boarding a submarine during drills. He has also stepped up efforts to expand his regime’s missile arsenal, personally overseeing the launch of “ultra-precision” guided missiles in June. North Korea is banned from developing ballistic missiles under sanctions imposed by the United Nations for nuclear testing.

Putting ballistic missiles on submarines may also limit Kim’s ability to control the weapons, Bermudez said.

“It also assumes that Pyongyang would entrust an operational nuclear-armed missile to the captain of a submarine who would, in time of war, most likely be out of communication with the leadership,” he said.

Atomic Bombs

North Korea may have made “considerable” progress in miniaturizing its atomic bombs, South Korean Defense Minister Han Min Koo said today at a parliamentary hearing. Army General Curtis Scaparrotti, the commander of U.S. forces in Korea, said last month that the North may now be able to miniaturize a nuclear weapon to fit on a mobile missile warhead that could hit parts of the U.S.

While Kim hasn’t yet deployed a ballistic missile that could hit the mainland U.S., “he’s showing us the signs that he’s trying to get there,” Admiral Samuel Locklear, head of U.S. forces in the Pacific, said in a Bloomberg Government interview in September.