Thursday, July 1, 2010

North Korean Semi-submersible craft

North Korea has developed a range of semi-submersible and submersible boats for special forces (including agents) infiltration. Some designs can carry lightweight torpedoes and therefore could be used for direct attack as well as transportation.
Relatively little is known in the public domain but we can piece together a simple evolutionary tree from the few captured examples and exported boats. These craft are in service with:
  • North Korea
  • South Korea (captured/copied)
  • Iran
  • Vietnam
  • Myanmar (TBC)
  • Venezuela (TBC)
Type-A (non-submersible)
Early infiltration craft were not submersible, relying on disguise as fishing craft to avoid detection. These are high-speed craft with fake superstructures to appear more humble. Some may have detachable superstructures to allow stowage in motherships which sometimes have a hidden hanger at the rear. This infiltration craft category is known as Type-A and likely continues to be used in addition to the more advanced craft discussed below.
Dimensions: L 11m, Displacement 3t
Speed: 50kts
Armament : Small arms and crew carried weapons, possibly including short range air-defence missiles and RPGs.
Although many successful missions are likely to have been accomplished, these boats were obviously considered too liable to detection, and so a more stealthy survivable infiltration craft was developed. The Submersible Infiltration Landing Craft (SILC) is essentially a speedboat which can submerge up to the deck thus reducing its visual and radar signatures.
Type-B / Racoon
The first SILC, now known as Type-B in the West, was first openly talked about after an example was captured in 1983 by South Korean forces. 
Dimensions: L 9.3m, W2.54, Displacement: 5 tons (est)
Speed: 30-40 kts surfaced; 12kts semi-submerged (est)
Range: 300nm surfaced (est)
Compliment: 3 (2x crew, 3 pax)
Armament: small arms

The captured Type-B craft was placed into service by South Korea and employed by the naval special forces (ROKN UDT/SEAL) as a covert infiltration craft known as 'Racoon' [sic]. This experience may have influenced the US military to start experimenting with submersible boats, albeit over 10 years later.
The South Koreans reverse engineered the craft and produced a number of boats which are likely still in service.
 

An improved variation of the Type-B with two smaller cabins has been reported by defectors:

Type-C (SP-10)
A general refinement of the Type-B, this could be regarded as a sub-variant. The designation was applied to a SILC captured by South Korea in 1990s and now on display in Seoul.

Dimensions: L 9.3m, W2.54m, Displacement : 5 tons
Speed: 30-40 kts surfaced; 12kts semisubmerged
Range: 300nm surfaced
Compliment: 6 (2x crew, 4 passengers)
Armament: small arms


I-SILC
The Improved-SILC represents a step-change in sophistication for DPRK infiltration craft. Possibly designated SP-10H. The I-SILC is fully submersible (i.e. a submarine) but approaches the shore at high speed on the surface like previous SILC. However, it can run almost fully submerged 3m below the surface with only the snorkel mast above the surface (the larger mast towards the rear of the boat). When not in use the snorkel folds aft to reduce the silhouette and radar signature.

In an emergency the boat can submerge completely to a depth of 20m (some sources say 25m) to avoid detection. The captured craft cannot travel forward underwayer because it lacks electric motors, but the I-SILC-Viet appears to have electric motors mounted on the rear diving planes for this purpose.

Three distinct variations are known in the open sources:
  • 1996/7 - 2 boats sold to Vietnam along with 2 midget submarines. Virtually unreported.
  • 1998 - Improved SILC sunk 150 kilometers southwest of Pusan. The body of a North Korean frogman was recovered nearby. The vessel was first spotted two kilometers off the port city of Yosu. Boat also salvaged and displayed. This boat is the first referred to as "I-SILC"
  • 2002 - 1 'Taedong-B' submersible torpedo boats exported to Iran
  • 2002 - 2 'Taedong-C' semi-submersible torpedo boats exported to Iran (quite different design)
In terms of evolution however the 1998 DPRK example appears the earliest model. The Vietnamese boat is half-way between that and the Taedong-B.

The 'Taedong-B' I-SILC sold to Iran is the most evolved design identified and feature torpedo tubes. It seems likely that there are more versions, some with torpedoes like the Taedong-B, in DPRK service. It is also likely, though unconfirmed, that DPRK has or will soon deliver I-SILC to Venezuela and Myanmar.

Specifications for recovered sunk DPRK I-SILC:
Dimensions: L 12.8m, W2.95m, Displacement: 10.5 tons
Machinery: 3x 250 or 260 hp V8 (Johnson/OMC, etc)
Speed: 40-50kts surfaced, 4-6 kts submerged
Range: 200nm
Diving Depth: 3m snorkeling, 20 m maximum
Crew: 8 (4x crew, 1-2 escorts, 1-3 infiltrators)
Radar: Japanese made Furuno 1830
Armament: small arms 


The I-SILC-Viet is longer than the I-SILC and has a more rounded upper deck. There appear to be electric motors for underwater movement mounted on the dive planes, although this feature has not been confirmed and an alternative hypothesis is that they are diver swimming aids. 
  
There are two models of Taedong submersible reported, -B and -C.

Taedong-B - Kajami
Known as "Kajami" in Iranian service (Kajami appears to be a Korean name however). The craft is more evolved than either the original "I-SILC" and the I-SILC-Viet, although closer to the latter, with a long curved stern, possibly showing Fabio Buzzi design influences (as do many Iranian small craft).

"Taedong" is an interim designation applied to some North Korean craft whilst their true designation is unknown, and probably relates to the shipyard. The ship carrying these boats to Iran was stopped and inspected by US forces so we can assume that USN is intimately familiar with the design now.

Taedong-B in Satellite imagery of North Korean port. Source Naval Open Source INTelligence (blog)

Taedong-C - Gahjae
A semi-submersible variant of the IPS-16 Peykaap torpedo boat. This craft is quite different from the I-SILC discussed above. Like the Taedong-B the type has two 324mm torpedo tubes. Relative to the Peykaap the Taedong-C has a redesigned bridge with single central window (vs the wedge-shaped double window of the Peykaap) with prominent splash board below the windows. The foredeck and stern are more hydrodynamically optimised than the Peykaap to assist semi-submerged running. The rear deck well is plated over and three exhausts protrude from it, canted inwards and aft.
Source: PressTV

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