North Korea Shows Off Previously Secret “Stealth” Missile Hover-Boat, Surface effect ship with low radar profile test-fires long-range anti-ship missiles. Article Link
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On February 7, 2015 the North Korean government’s official news service published images of the test-firing of new homegrown anti-ship missiles from a new class of ship that the Korean People’s Army (KPA) Navy has reportedly had in development for over a decade. While details are thin, the vessel is an attempt by the North Koreans to develop a high-speed “stealth” ship-killer using a surface effect hull—a combination of catamaran and hovercraft. This is the first time the ship and the missiles it fired have been shown by North Korean state media. The implied threat of the new craft and its missiles is that North Korea could strike at South Korean and US naval vessels near its territorial waters without warning.
The KPA has long had a love affair with hovercraft, though most of the KPA Navy’s air-cushion ships are traditional hovercraft with large propeller fans. Surface Effect Ships (SESs) have a pair of rigid outer hulls surrounding a central air-cushion system that allows them to skim along the surface of the ocean and use more efficient marine propellers. Earlier, smaller KPA Navy SES patrol craft have reportedly reached speeds of 50 knots (90 kilometers per hour, or 57.6 miles per hour) and have incorporated some “stealth” features, such as faceted hull and superstructure designs intended to reduce their radar reflection.
However, the new SESs are bigger—as much as 40 meters (131 feet) long—and carry four of a new class of anti-ship missile derived from the Russian-made Kh-35 Uran—a sea-skimming missile with a range of over 250 kilometers (135 nautical miles) similar to the US’ Harpoon missile. It’s not known if the North Korean built version has that sort of range, but during tests it was said to have hit and sunk a target ship 100 kilometers away. The SES is also equipped with two North Korean AK-630 30mm Gatling gun close-in weapons systems, four machine gun turrets, and a short-range anti-aircraft missile system.
Two more of the new class of SES are under construction, though they each appear to have different gun configurations—with one appearing to have a 76mm main gun similar to the OTO Melara gun system carried on many of the world’s small combatant ships.
The North Korean Surface Effect Ship (SES) is known as the Nongo class by the US Department of Defense. One side of Nampo Naval Base is used to build, modify, and refit ships. This side of the base is also the site of the Naval commands (NAVCOM) headquarters building. Various naval construction halls are present, including those used for newly constructed North Korean Surface Effect Ship (SES). The import by the DPRK of the Kh-35E anti-shipping cruise missiles was first disclosed in early 2012 in a North Korean video of an SES showing racks used to mount four Kh-35 canisters.
This Fast Attack Craft appears to have significant radar signature reduction characteristics. Torpedo boats with these features were exported to Iran in about 2002 (Tir and Peykaap classes). The armament on this craft appears to include a 57mm [56mm?] medium caliber main gun mounted on the foredeck, and a smaller 30mm AAA turret on the aft deck.
The hull is very wide, suggesting that it is a surface effect ship (SES) similar in principle to the infamous Soviet ‘Bora’ class, or the more modern and stealthy Norwegian Skjold class. News reports suggest a 90km (50kts) speed. North Korea has a large number of hovercraft which it has been producing since 1987, but in this case the absence of visible external propulsion points away from ‘pure’ hovercraft and towards SES.
In addition to the Nongo type there are at least two similar boats on the West coast clearly visible on Google Earth satellite imagery. The boats do not match any known type. The hull proportions generally match the Nongo type but are possibly slightly shorter (35m v 38m) and clearly non-stealthy. Although the two West coast boats are very similar to each other they have significant differences suggesting that they are two separate but closely related types.
The “Type A SES” is probably a reasonably capable missile boat of relatively recent construction. The layout follows the standard Russian pattern, with the missile tubes beside the bridge firing forward, and a long superstructure extending rearwards almost to the stern. There appears to be a medium caliber gun on the aft deck but something smaller, probably a 30mm CIWS, to the bow. The arrangement with the ‘main’ gun at the rear is again more typical of Russian missile boat designs than Western ones.
The “Type B SES” differs from “SES-A” in having a more squared bow, the medium caliber gun at the front not back, and a more separated superstructure. The anti-ship missile mountings are clearly visible.
One of the primary objectives in boat design is to reduce the amount of drag caused by the interface of the hull with the water surface. Early planing hulls were designed so that forward motion of the hull raised the vessel to cause it to ride on a smaller portion of its hull surface resulting in reduced hull-to-water friction. The design of hydrofoil vessels further reduced hull contact with the water by attaching foils to the hulls upon which the boats ride at high speed. Some marine vessels interpose a film of air between the vessel’s hull and the water to reduce the hull-to-water friction.
Two primary types of high-speed advanced marine vehicles are the surface effect ship (SES) (or surface effect vehicle (SEV)) and the fully skirted hovercraft. Both are considered air-cushioned vehicles (ACV) in that each rides on a pressurized cushion of air. Surface effect ships were an improvement over the air film hulls as the hulls of surface effect ships are raised out of the water by a pressurized air cushion that is partially captured within the hull of the vessel.
The prior art of air cushion vessel hull designs contained the air cushion with flexible seals, which are a rubberized curtain, either all around the vessel as in the case of the hovercraft air cushioned vessels, or across the front and the back of the vessel with thin parallel side hulls that provide a side seal for the air cushion as in the case of surface effect ships. The flexible seals reduce the amount of air lost from the air cushion but create a rough ride, “a cobble stone ride,” even in smooth water. As the surface of the water becomes rougher the flexible seals can be separated from each other, causing further deterioration in ride quality. Also, in rough water the flexible seals frequently fail to maintain the air cushion, causing the craft’s hull to drop lower into the water until the seal is regained and the air cushion is reestablished.
The large and medium operative surface effect ships are equipped with a heavy machinery to transfer the power of the engines to the lift fans and the propellers, to provide with required flow volume, cushion pressure and thrust. The machinery of these ships is heavy, mechanically complicated and consists of many multilink driving shafts, clutches and reduction gears. Typical of such surface effect ships are LCAC, built by Textron Marine Systems, USA, and SR.N6, SR.N4 built by British Hovercraft Corp., Ltd., United Kingdon. In the SR.N4, for instance, driving shafts from the engines to lift fans are 18.3 meters long.
The air cushion of the SES or SEV is contained on the sides by relatively thin, rigid, lateral walls contacting and protruding into the water, and at the front and rear by flexible or semi-flexible seals or skirts. Though the hovercraft skirt theoretically can have a lower drag due to the air gap which would give no interaction with the surface, in reality considerable drag can be experienced in rougher water due to wave interaction with the skirt’s fingers.
The SES will have considerably lower hydrodynamic drag in rougher water due to the thinness and rigidity of the side-walls as opposed to the unwieldy side portion of the skirt of the hovercraft. A further advantage of the SES is that since its side-walls protrude below the water surface there is practically no air loss out the sides. The reduced drag of the SES reduces the thrust required to achieve a given speed, and the reduced air loss reduces the power required for the lift fans. In addition, water-jet or other water propulsion means may be employed with the SES which are generally more efficient than air-propellers on hovercraft. Also, the operational costs of the side-walls on the SES are much lower when compared to the side portions of the skirt of the hovercraft.
North Korean Kh-35 Clone
North Korea announced in November 2020 that it had completed deployment of its Kumsong-3 anti-ship missiles to naval bases and ships on both the east and west coasts. This new missile is intended to protect North Korea’s surface ships and submarines from hostile (South Korean, American and Japanese) warships. More test firing was to take place before the end of 2020 but so far that has not happened.
Kumsong-3 was first revealed in 2014 when North Korea released a video showing the missile. The first test firing took place in 2015 when one was launched from a patrol boat and observed landing 200 kilometers distant. During an April 2017 military parade in North Korea Kumsong-3 was shown mounted on a tracked vehicle, which carried four storage/launch cannisters side-by-side. A few months later one of these vehicles on the east coast fired four Kumsong-3 missiles. South Korea, the U.S. and Japan monitor both coasts for such launches and noted that these missiles travelled 240 kilometers.
It was obvious (from the pictures) that the missile was a Russian Kh-35 (also known as the SS-N-25 or Switchblade) that had earlier been seen on one or two of the four of five large (over 1,000 ton) surface warships the North Korean Navy has that were capable of going to sea, but rarely do. The 2017 test was from a mobile launcher and that was apparently the same one that had appeared earlier in the parade. The missile shown not only looked like a Russian Kh-35 and the data North Korea released showed it performing like a Kh-35, which Russia has been busy upgrading and marketing since the late 1990s.
The Kh-35 was the Russian response to the American Harpoon and development did not begin until 1983. Work was stalled with the collapse of the Soviet Union in 1991, which saw most of the defense budget disappear as well. Russia announced the Kh-35 was available for export in 1996 but the Russian Navy did not start using it until 2003 and that was about when export sales and deliveries began to happen. In 2006 Russia announced it had put into service a land-based version of Kh-35 that could be operated from fixed or mobile (trucks or tracked vehicles) launchers. This is what North Korea did with its Kumsong-3 in 2017.
By 2008 the Kh-35 could be fired from helicopters, aircraft, ships, or land. It is a 620 kg missile that used a rocket booster for launch and then switches to a small turbojet. The missile flies 10-15 meters above the water. When making its final approach to a target the missile drops to about four meters above the water. The earliest version had a range of 120 kilometers but the 2008 upgrade increased that to 250 kilometers. That increased Kh-35 weight to 670 kg. Russia sells them to export customers for less than a million dollars each.
Russia denies it sold the missiles to North Korea thus the only other likely source is one of the known foreign customers (Algeria, Azerbaijan, Burma, India, Iran, Venezuela, and Vietnam). Vietnam is building Kh-35 under license and Iran may be doing so without a license. Iran could have sent one or two Kh-35s to North Korea as the two countries have long exchanged missile tech, via air freight in the knowledge that North Korea had the resources to build its own unauthorized copies. Myanmar (Burma) is also known to share such information with North Korea. The few Kh-35 clones seen in action could be using 1970s technology to do what they obviously did. These missiles use a simple jet engine and travel at up to 700 kilometers an hour. They can use inertial guidance or GPS and be programmed to change course. Terminal guidance can be as primitive as a 1960s era radar homing system or a more modern heat seeking system. Kumsong-3 tests indicate that the North Korean missile had an improved heat seeking terminal-guidance system. Kumsong-3 did have the longer range of the late model Kh-35.
The Kh-35 is similar to the American Harpoon, but is lighter than the 691 kg (1,600 pound) Harpoon and has similar range, which is 224 kilometers for the latest Harpoon version. The Harpoon entered service in 1977 and became one of the most widely used (and emulated) anti-ship missiles in the world, mainly because of reliability and constant upgrades. A 2015 Russian upgrade for the Kh-35 extended range to 260 kilometers and improved the guidance system by adding two-way communications for course changes and improved terminal homing.
The 2017 Kumsong-3 test was given considerable media exposure by the North Koreans. They knew that these tests are closely watched by the U.S., Japan and South Korea. North Korea wanted everyone to think that they had something similar to the latest (2015) version of the Kh-35. But it was also possible that all they had done was extend the range (a simple mod) and used an older terminal guidance system. North Korea had a small target ship out at sea, equipped with a radar enhancement device, which made the ship look larger, as if to imply an American destroyer or carrier. The North Korean target was not moving and had no countermeasures. In combat Western warships, which have lots of experience with missiles like this, have countermeasures and use them regularly in training.
