Yechŏn-class frigate
 4-view diagram of Yechŏn in 2007.
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| Class overview | |
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| Builders: |
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| Operators: | |
| Preceded by: | Ansa-class frigate |
| Succeeded by: | Chunchŏn-class frigate |
| Built: | 2003-2014 |
| In commission: | 2006-present |
| Completed: | 18 |
| Active: | 18 |
| General characteristics (Yechŏn, 2007) | |
| Type: | Frigate |
| Displacement: | 4,800 tons full load |
| Length: |
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| Beam: |
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| Draught: | 5.18 m to keel |
| Propulsion: | |
| Speed: | 34 knots |
| Range: | 4,400 nautical miles (8,150 km) at 15 knots |
| Complement: |
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| Sensors and processing systems: |
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| Electronic warfare & decoys: |
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| Armament: |
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| Aircraft carried: | 1 × GH-28 Ppulsoeori |
| Aviation facilities: |
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The Yechŏn-class frigates are a class of warship built in Menghe during the 2000s and early 2010s. Eighteen were built in all, sixteen for domestic use and two for export to Idacua. The last ten ships (including both export models), starting with Dŏkju, are often considered a separate subclass due to their revised armament and countermeasures. The Yechŏns were succeeded by the Chunchŏn-class frigate, but the type remains in service and is still considered highly capable in the fleet escort role.
Role
The Menghean hull type of the Yechŏn-class is HO, for Oechŭng Howiham (외층 호위함 / 外層護衞艦), or "outer-layer escort ship." This hull classification was first applied to the Ansa-class frigates, to distinguish them from the larger Pyŏng'an-class destroyers. The Yechŏns, however, were the first Menghean frigates to fully exemplify the HO type.
As the name implies, outer-layer escort ships are designed as defensive escorts for a carrier battle group, amphibious battle group, or convoy, and would either form an outer defensive ring around the protected unit, or position themsvelves on the threat axis between the protected unit and a suspected enemy. They are primarily designed around the anti-submarine role: "main force escort ships" (Juryŏk Howiham) provide the long-range anti-air umbrella for the escorted formation, and engage any submarines which pass through the outer escort ring.
Because they can rely on other ships for long-range air defense, outer-layer escort ships in Menghean doctrine are not armed with long-range air defense suites. Their outer position, however, puts them between the main fleet and any enemy threat, and makes them vulnerable to being picked off ahead of a larger strike. For this reason, ships in this design require a highly capable short-range air defense system, even as they lack long-range air defense capabilities. This requires a fast-scanning radar high on a mast (to extend the distance to the radar horizon and a short-range surface-to-air missile armament which can engage many low-level targets in rapid succession. This distinguishes outer-layer escort ships from medium anti-submarine patrol ships, like the Ginam and Mirun classes, which have minimal anti-air armament as they are designed to patrol areas with a reduced enemy air and surface threat.
The final constraint on the type is cost. Because of its intended role of escorting a high-value target at the outer ring of a formation, the Yechŏn class and its successors are likely to suffer high attrition in the event of a war. To increase the number of outer escorts, and reduce the blow inflicted by each loss, designers were pressured to leave out any capabilities not directly relevant to the above mission. Thus, the class's capabilities for coastal bombardment, special forces insertion, mine clearance operations, and littoral combat are very limited, and in the class's initial iteration, so were its anti-ship capabilities.
Development
Preliminary design work on a new frigate class began in the mid-1990s, while work on the Ansa-class frigates was still underway. The Navy solicited a range of designs, under the common heading of "New Century Warship" (Sinsedae Jŏnham), but tight defense budgets during the late 1990s and early 2000s meant that no definitive orders would be placed until 2002. Many of the more ambitious designs, including one Plan 83, incorporated the Glasic Mark 41 Vertical Launching System and LM2500 gas turbine, but Tír Glas remained noncommital about whether to sell or license these systems due to objections from Dayashina. Menghean naval procurement staff viewed the former system as particularly important because the Ansa and Hawŏn classes had YDG-37 (licensed Uragan missile systems, but with single-arm launchers and SARH guidance that greatly limited their effective target engagement rate. The noisy HŎ-2 Poksŏl anti-submarine weapon was also in need of replacement.
A breakthrough came in 2001, when Choe Sŭng-min agreed to resolve the Renkaku Islands dispute with Dayashina as part of a debt forgiveness deal following the 1999 Menghean financial crisis. This settled a lingering source of tensions between the two countries, and led the Dayashinese government to green-light arms sales of less-sensitive equipment to Menghe. With that technical hurdle cleared, the Menghean Ministry of National Defense authorized the construction of six frigates of the Plan 83 type. The contract specified that three would be built by the Gyŏngsan Songsu-do Shipyard and three by the Kimhae Naval Yard in Donggyŏng, to keep both facilities in operation during a period of modest spending.
Characteristics
Propulsion and machinery
The ships of the Yechŏn class are powered by a CODOG powerplant comprised of two LM2500 gas turbines developing 33,600 shp (25,100 kW) each and two Samsan S9000H diesel engines developing 8,000 shp (6,000 kW) each. Each propeller shaft is coupled to one gas turbine and one diesel engine by a simple clutch-type gearing unit. When running the gas turbines at full power, the ships can generate 67,200 shaft horsepower of output, for a top speed in excess of 32 knots.
Auxiliary power consists of three 1,500 kW Samsan S870 diesel generators, all grouped in a single machinery room forward of the turbine space. These power the ship's systems and assist in engine startup, though they cannot provide power to the propeller shafts.
All components of the powerplant are built on special raft mounts to limit transmission of vibration to the hull, reducing the ship's acoustic signature to shield it from submarines. Prairie-Masker systems on the propeller blades and hull sides provide an additional layer of acoustic damping. All powerplant components can also be removed through the ship's funnel for maintenance or replacement.
Armament
Along with the Haeju-class destroyers, the Yechŏn-class frigates are the first Menghean warships to carry the Mark 41 Vertical Launching System. The four baseline Yechŏns and four improved Yazdans have two strike-length modules aft, rotated parallel to the path of travel, and two self-defense-length modules forward, mounted perpendicular to the path of travel. This results in a total of 32 VLS cells. In Yechŏn's as-built outfit, the forward 16 cells would be loaded with YDG-7G short-range surface-to-air missiles in single cells, and the aft 16 cells would carry eight HŎ-3 Ryongorŭm anti-submarine rockets and eight YDG-60 medium-range surface-to-air missiles.
The YDG-7G missile has an active radar seeker, meaning that it can independently acquire and engage a target without the need for illumination from the ship. Instead, it relies on inertial guidance and mid-course command updates to approach the target, with terminal homing from its own seeker. Combined with the use of a vertical launch system, this allows the Yechŏn-class to engage more simultaneous incoming threats than the Ansa and Hawŏn classes, which were limited to two simultaneous illumination targets in most directions and one missile launch every 6 seconds. The smaller short-range missile loadout - 16 missiles as opposed to 48 - was a more serious source of concern, pushing the development of the quadpacked YDG-7N.
As designed, the ships carried anti-ship missiles in box launchers on the deck space between the funnel and the forward superstructure. A typical 2000s loadout consisted of eight YDH-26 missiles in two quadruple boxes, though starting in 2016 some Yechŏn-class frigates have been refitted with the larger YDH-29 Chŏngryong supersonic anti-ship missile.
Apart from the HŎ-3 missiles in their aft VLS group, the Yechŏn-class frigates carry two forms of anti-submarine armament. On either side of the aft superstructure, below the Bulkkot CIWS mounts, are two twin 350mm torpedo tubes for the YŎ-35/2 torpedo. These are trainable twin-tube units, and they are stored behind roll-down metal covers when not in use to reduce radar reflections and protect the torpedo room from the elements. Forward of the superstructure, flanking the forward VLS group, are two HBDJ-21/12 rocket-propelled depth charge projectors. With a range of 4000 to 6000 meters using anti-submarine ammunition, these are of limited use against submarines, and in practice they are typically loaded with H-21ŎDG or ŎDN anti-torpedo rounds.
Gun armament consists of a single HP-76/1 76mm gun turret forward. This is directed by an MR-123 fire-control radar on the superstructure, and can be used against surface targets, aircraft, and anti-ship missiles. Its shore bombardment capability is limited. Two GBM-23/5 Bulkkot CIWS mounts, one on either side, provide additional close-range defense, though they cannot cover the 10-degree arc directly ahead of the ship.
As built, the first four Yechŏns were fitted with HBDJ-6/7 anti-frogman grenade launchers. These were not mounted on Yazdan, and during the late 2000s they were removed from the first group of ships as well.
Sensors and countermeasures
The main mast of the Yechŏn class carries a SMART-S 3D air search radar. This system has a range of 150 kilometers at 27 RPM, or 250 km at 13.5 RPM, though the former mode is used more frequently. Mounted 27 meters above the waterline, it can detect sea-skimming anti-ship missiles from a range of slightly over 30 kilometers.
On the aft superstructure, all Yechŏn class destroyers before Dŏkju are fitted with two STIR 2.4 radar illuminators. These mainly exist to provide terminal guidance for the YDG-60 (SM-2) anti-air missiles, though they can also illuminate targets for the YDG-7. Though the YDG-7 has its own active radar seeker, backup illumination improves its performance against jamming, chaff, and other countermeasures. Because the Yechŏn class is fitted with the Dayashinese Suijin Combat System (Menghean designation Susin) and two D-104 datalinks, it is possible for a Yechŏn-class frigate to provide terminal guidance to YDG-60 missiles fired from a different ship, such as a Haeju-class destroyer. In the expected role of a HO-type outer escort, this would allow the core battlegroup ships to maintain radar and radio silence while a Yechŏn-class frigate reveals its location by using search and illumination radars.
On top of the bridge is a single HR-280 surface search radar. While normally associated with anti-shipping surface combatants, such as the Chŏndong-class destroyers, this radar is also useful for detecting surface vessels and low-flying threats for defensive purposes. Under favorable atmospheric conditions, it can purportedly detect surface targets at a range of 250 kilometers in active mode and 400 kilometers in passive mode, but its practical range is limited by the degree of atmospheric ducting.
Aviation facilities
All Yechŏn-class destroyers, across subclasses, are equipped with a hangar for a single Gyundoan-Han GH-28 Ppulsoeori helicopter for anti-submarine duties. The landing pad is fitted with a hauldown device for recovering helicopters in rough seas, and it can be rigged with a net to prevent landed helicopters from sliding. The magazine forward of the helicopter hangar is shared with the torpedo launcher room: both the helicopter and the torpedo launchers use the same YŎ-35/2 torpedo.
Yazdan subclass
Upon reviewing lessons from the Battle of the Aqaba Sea, Menghean Navy doctrinal planners concluded that inadequate short-range missile defenses were responsible for the loss of the destroyer Bŏmram and the frigate Bupyŏng in air-launched missile strikes. To address this issue, they ordered that subsequent Yechŏn-class frigates be completed with a 24-missile YDG-61 launcher on top of the helicopter hangar, facing aft. This, in turn, required strengthening the hangar structure and raising the aft missile illumination radar, meaning that the changes could not be applied to ships already under fitting-out. The first ship built to the new standards would be Yazdan (sometimes transliterated Yajjdan), laid down in late April 2006.
Yazdan and the three ships that followed her (Hongsa, Pyŏngsŭb, and Buyŏ) are sometimes considered a separate subclass, due to their enhanced missile armament, reinforced hangar, and modified profile. Interestingly, however, the Menghean Navy did not issue a separate class name for this group, as it had done with the Hyŏngnam-class destroyers (a Yobu subclass) and Hawŏn-class frigates (an Ansa subclass), or for that matter the Dŏkju subclass which followed. Instead, Menghean sources sometimes refer to them as a "modified Yechŏn group" or "Yechŏn variant."
The initial report leading to the Yazdan subclass suggested that similar refits be made to existing ships, though this likely would have required a lighter YDG-61 launcher or serious rebuilding, if it were practical at all. In 2008, however, the development of the YDG-7N missile meant that the forward Mark 41 self-defense cells could be loaded with quad-packed surface-to-air missile canisters, increasing the maximum SAM loadout of the forward cells from 16 missiles to 64. This was, in practice, excessive, and most actual loadouts carried 36 or 48 missiles forward. Such a change was judged adequate to eliminate the need for a secondary YDG-61 launcher, even as Yazdan was still in fitting-out.
Dŏkju subclass
Beginning with HO Dŏkju, laid down at the end of 2007, the Menghean Navy switched to a new design with a revised superstructure and armament arrangement. Unlike the Yazdan group, this variant was designed from the keel up for major changes, and the Menghean Navy treats it as a separate ship class.
The main change involved replacing the self-defense-length vertical launch cells forward with strike-length modules. This required the addition of a raised platform extending forward of the superstructure, as the new VLS cells were a full deck longer than the old ones and could not be recessed further into the hull. This revision allowed more flexibility in the choice of payloads: eight to twelve forward VLS cells could be loaded with YDG-7N or YDG-64 surface-to-air missiles, leaving the rest for other strike-length payloads.
The other major change involved the rearrangement of the STIR 2.4 illumination and guidance radars on the superstructure. While the Yechŏn and Yazdan groups both had the directors facing aft in a superfiring arrangement, the Dŏkju and successors have one dish forward and one aft, for 360-degree coverage and continuous tracking of targets that fly across the bow. The forward STIR director is also capable of calculating firing solutions for the ship's 76mm gun and correcting fire by tracking outgoing rounds.
The Dŏkju subclass also has minor improvements to the electronic warfare suite, with a JJ-9 combined ESM/ECM antenna on either side of the mast, Baram-2 chaff, flare, and decoy launchers replacing the bulkier Baram-1 mounts, and four Mungu floating radar decoy launchers added in pairs flanking the funnel. The communications suite is also improved, with a FSO laser communication array on the main mast and a passive ESM detection and classification tower in front of the aft fire-control radar.