North Korean Sang-O submarine captured by South Korea in 1996.

Something very strange has happened on the Korean peninsula.  More than 50 North Korean submarines — about 70% of the country’s known fleet — have reportedly left their bases and disappeared from South Korea’s military radar.  They also represent most of the North Korean Navy, which in addition to submarines, has relatively few surface combatants, roughly a half dozen frigates and an equal number of corvettes. What makes the deployment of the submarines even odder is that it coincides with a de-escalation of tensions between the two Koreas.  On Monday, the two countries announced a plan to lift the “semi-state of war” prompted by a land-mine explosion that injured two South Korean soldiers on August 4.  The two countries are technically at war, living under a cease-fire agreement since 1953.

The North Korean submarine fleet is a mix of old surplus submarines from Russia and China along with newer but smaller submarines built in North Korea. North Korea imported over 70 Soviet designed Romeo class submarines. It is generally though that 22 or more of theses are currently in operation. The Romeo class submarines were designed and built in the 1950s and have a range around 9,000 miles. They are generally considered to be obsolete, though potentially useful for training or surveillance.

The largest component of the North Korean fleet may be Sang-O class submarines. This class of submarines was built in North Korean shipyards. They are smaller than the Romeo class submarines and are believed to have a range of around 1,500 miles. A larger version, Sang-O II, has also been commissioned. A newer submarine design, the Sinpo class, is also believed to be under construction.

The South Korean news agency Yonhap quoted a military official as saying the country was “mobilizing all our surveillance resources” to find the missing subs. “No one knows whether the North will attack our warships or commercial vessels,” the South Korean official reportedly said.  The South Korean Navy supported by the US is actively looking for the missing submarines.

Last May, North Korea claimed to demonstrate their first Submarine Launched Ballistic Missile (SLBM.) Experts questioned the authenticity of the recent test, suggesting that the photos of the launch have reportedly been digitally manipulated.  Others have also suggested that the missile was probably fired from a sunken platform rather than an underwater submarine.