Tensions have been mounting on the Korean peninsula since a North Korean landmine seriously injured two South Korean soldiers on August 4.
That incident led to spiking tensions between the two countries, culminating in limited artillery exchanges and North Korea’s placing of its front-line troops on a war footing.
Tensions relaxed earlier this week when North Korea issued an apology for the land mine after tense negotiations. But there are still concerns over Pyongyang’s ultimate end goal during the escalation. Just as Pyongyang was apologizing for the incident, 70% of its submarine fleet disappeared from South Korea’s radar, meaning North Korea had deployed some 50 vessels.
The missing subs were cause for alarm in South Korea. “The number is nearly 10 times the normal level … we take the situation very seriously,” an unnamed South Korean government spokesman told the AFP.
Since the deployment of the submarines earlier this week there have been signs that North Korea may have recalled the vessels. Vice reports that there are signs that a number of the submarines have returned following deployment, according to a South Korean official.
Kim Min-seok, a defense ministry spokesman for South Korea, likewise said that the submarines are believed to have returned to their pens in North Korea, according to Fox. But until Seoul can be totally sure of the vessels’ location and intent, the country will remain at a heightened alert.
“We’ve said before the disappearance [of North Korean submarines] is a source of concern, and the fact is they are not easy to detect when they are submerged under water,” Kim said.
“No one knows whether the North will attack our warships or commercial vessels,” the unnamed defense ministry official added.
Pyongyang’s deployment of its submarines was likely an attempt to put pressure on South Korea during the landmine attack-related negotiations earlier in the week, Moon Geun-shik, a defense analyst at the Korea Defense and Security Forum, told The Chosun Ilbo. Now that the negotiations have concluded, the submarines would likely return to port.
Age and obsolescence might also explain why the vessels have returned to port.
The Diplomat notes that Pyongyang’s fleet of rusting diesel submarines is capable of little more than coastal defense and has limited offensive capabilities. North Korea has approximately 70 submarines in its fleet, but 20 are Romeo-class submarines built with 1950s technology. Another 40 are North Korean domestically developed Sang-O-class subs that were specially developed for the insertion of special forces into South Korea, along with mine deployment. The rest of the fleet is thought to be comprised of Yono-class midget submarines with limited range, firepower, and operating depth.
All of these submarines are diesel-electric and extremely old. As such, the submarines can submerge for only a few days at a time — and once they surface, it would easy for South Korea to be able to pinpoint their location. Even with many of the subs still missing, their operational limitations lend credence to the idea that at least a portion of the submarines have returned to their pens in North Korea or are continuing to hide out in secluded coves and inlets throughout the North Korean shoreline.
But despite the submarines’ age and relative technological inferiority, the vessels could still cause substantial damage to South Korean vessels and disrupt shipping throughout the peninsula. In 2010, a North Korean submarine destroyed the Cheonon, a South Korean naval vessel. The attack killed 46 South Korean sailors.
The sinking of the Cheonon is a stark reminder of the asymmetrical challenges that North Korea’s massive — albeit rotting — diesel submarine fleet presents.
They even has some tactical advantages over more advanced submersibles. Diesel submarines are significantly quieter than any other seaborne vessel. Although they cannot operate all that well in the open ocean, North Korea could still plant its submarines along major coastal transport and trade routes without Seoul being able to detect them.
“Picking up the quiet hum of a battery-powered, diesel-electric submarine in busy coastal waters is like trying to identify the sound of a single car engine in the din of a major city,” US Rear Admiral Frank Drennan warned in March 2015.
For this reason alone, North Korea’s submarine fleet remains a major threat — however decrepit it may be.