May 20, 2015

South Korea's Undersea Anti-Submarine Sensor Network - Part of SEAWEB

North Korea Naval Bases and Fleet HQs. One might expect mini-submarines to operate out of Sagin Ni (under West Sea Fleet Command). Sinpo - Mayang Do and Chaho are listed as Submarine Bases (under East Sea Fleet Command).

The SEAWEB Network goes by other names such as Fixed Surveillance System (FSS large PDF file - see pages 128-129) (, older term IUSS and oldest (SOSUS). SEAWEB includes sonar, LIDAR, optical CCTV, infrared, chemical sniffing and SIGINT amongst other sensors. (Courtesy US Navy in 2006, but since then the revolution in sensor technology and data management and storage has made SEAWEB a major unsung Western asset. South Korea's undersea sensor network is just one local branch of SEAWEB.)

South Korea has had a fixed undersea sensor network for more than 60 years. This would have started with the US Navy installing seafloor SOSUS arrays and magnetic anomally-indicator loop technically. Two shocks, the sinking of ROKS Cheonan in 2010 and North Korean moves in May 2015 toward an SLBM capability, have increased attention on South Korea integrating its undersea sensor into the Kill Chain strategy and infrastructure.

The US Navy and the NSA with its supercomputers would have worked with South Korean equivalents on the collection and easy retrieval of vast amounts of data collected from the undersea sensor system. Data management is a major aspect of the US Navy-NSA SEAWEB network - which could provide thousands of data signatures of North Korea, Chinese and Russian submarines and surface shipping. SEAWEB might be seen as a highly secure Intranet where membership /participation is tied to alliance with the US. Sometimes the US would like allies to buy alot of American hardware as part of the alliance membership status. It may be that South Korean submarines would need enough of the correct computer hardware and software "keys" in SK combat systems to access the SK branch of SEAWEB. 

For possible positions of the SeaWeb as it covers East Asia see Submarine Matter's How to Trap the Chinese Dragon - SeaWeb's Fixed Undersea Array, September 4, 2015.

As a political reaction South Korea's leadership talks of new beginnings regarding the undersea sensor network, but the network has steadily evolved in capability and in geographical extend since the early 1950s.

The following are portions of a May 13, 2015 South Korean Korea Joongang Daily, article indicating South Korea intends to extend its undersea "Kill Chain" infrastructure to handle the emerging North Korean SLBM threat :

"South’s military says ‘Kill Chain’ can be extended under water...Defense Ministry spokesman Kim Min-seok …said the South has the capability to track down North Korean submarines in real time when they are in naval bases. “If we concluded that a SLBM-capable submarine is a threat, we can pre-emptively take it out.”

The military also decided to improve its systems to detect the North’s SLBMs and upgrade submarine warfare capabilities. A military official said the modifications will be made based on the “4D Strategy” to detect, defend, disrupt and destroy North Korean threats, introduced by Commander Curtis Scaparrotti of the Korea-U.S. Combined Forces Command.

The two countries aim to create an operational plan based on that strategy and it is expected to include a plan to shoot down an SLBM-capable submarine of the North.

“We have an underwater interception system to counter the North’s submarines,” said the official. “Our military can operate Kill Chains both in the air and under water. We will improve our sonar abilities in the future.” 


Reports of South Korean sensors to counter mainly North Korea submarine and ship incursions have concentrated on South Korea's response to the March 2010 NK midget submarine sinking of ROKS Cheonan. But South Korea and the US would have installed undersea sensors against North Korea since the early 1950s.

The fixed undersea sensor network complements mobile undersea elements including South Korean, Japanese and US submarines, AUVs, LDUUVs and air dropped sinking sensors.

As well as undersea sensors South Korea operates ground stations, naval surface vessels and aircraft as well as interacting with US satellites and stealth drones. All these that operate infrared, optical, sonar and radar sensors to detect when North Korea submarines leave North Korean naval bases or when submarines might fire missiles. SIGINT including traffic analysis would also prove productive before, during and after submarine operations. 

Strategypage has provided several articles in 2010, 2011 and 2014 on South Korea's "SOSUS (SOund Surveillance System)" but there are many more sensor types that have been installed into South Korea's sensor network over the decades. 

The undersea system would not be limited to active and passive sonar but could utilise other sensors including:

-  magnetic anomally-indicator loop sensors which has been widely used by countries since WWII onwards  
-  vapour-chemical sniffing sensors
-  fixed undersea LIDAR
-  infrared undersea CCTV, and
-  seafloor, tethered and floating SIGINT intercept.

The Cheonan sinking would have underlined the South Korean and US need to provide many more undersea sensor arrays and nodes to make the network more sensitive, and quicker reacting to  North Korea midget submarines on battery, diver propulsion vehicles, torpedos and SLBM launches. North Korea submarines and diver vehicles operate near the South Korea coast and islands with the expectation that landform and shallow water "clutter' would mask their movements.   

In January 2011 it was reported: "South Korea's military is planning to install underwater sensors near frontier islands in the Yellow Sea to guard against attacks by North Korea's submarines. "We plan to install a number of underwater sensors to beef up defence capability in strategically important north-western islands like Baengnyeong and Yeonpyeong following the sinking of the Cheonan warship," an unidentified senior military official said. The sensors will be monitored from a control centre located on Baengnyeong island, the closest one to the border with North Korea, according to Agence France Presse."

The need to detect North Korean SLBM launches from North Korean naval bases would logically require sensors to increasingly focus on submarine activities within those bases. 

Even for an individual North Korean submarine operation South Korea and the US can lay surface vessel and air-dropped sonar buoys working to ground station, vessel and satellite - and in turn tying in with undersea sensors already there. Towed sensor arrays are also used.

Seafloor-upward floating or upward propelled mines/torpedos can be launched on command (including in peacetime) of automatically be activated/tripped in time of war. The sensor signatures give off by North Korean vessels would be relevant. 

Japan's undersea sensor network also faces the North Korean menace. Some aspects of Japan's network will be described next week.



Anonymous said...

Dear Pete,

do the South Korean submarines then have access to the SEAWEB network without a US combat system?


I have these feeling that the North Korean launch was a fake.

Here the official news report:

At 2:56 you can see a ship nearby. This ship is missing in the next pictures and also the picture with Kim Jung Un and the missile in the background is unrealistic. He must have been incredibly close to the launch site.

P.P.S: Another link

Peter Coates said...

Hi MHalblaub

I'd guess South Korea would need enough of the correct computer hardware and software "keys" or "handshakes" to access the South Korean portion of SEAWEB. Probably not the nearby Japanese portion.

Probably best to think of SEAWEB as a highly secure Intranet where membership/participation is tied to alliance with the US. Sometimes the US would like allies to buy alot of American hardware as part of the alliance membership fee.

Germany and other NATO members would face similar issues on SEAWEB in the North Atlantic and Baltic.

PS. Yes looks mightly suspect. A real missile would be too close if it went off course and had to be destroyed by the range safety officer.

PPS. Yes what Eric has recorded at is true. Many in our Navy want a sub with all the features possible even if some are rarely used. Australia expressed happiness with the 3,000 ton (surfaced) Soryu but it is unclear whether Australia expects the 216 and Ocean to weigh 4,000 tons surfaced to carry all possible features.