Mirun-class corvette

3-view diagram of Mirun in 2008.
Class overview
Operators:	Menghe
Preceded by:	Ginam-class frigate
Built:	2005-2013
In commission:	2008-present
Planned:	10
Completed:	10
General characteristics (Mirun, 2008)
Type:	Anti-submarine corvette
Displacement:	2,200 tons standard 2,640 tons full load
Length:	106.1 m overall 99.9 m at waterline
Beam:	13.7 m at waterline
Draught:	3.66 m to keel
Propulsion:	CODAG 2 Samsan S9000H diesel engines (8,000 shp each) 1 LM2500 turbine (30,000 shp)
Speed:	30 knots
Range:	4,400 nautical miles (8,150 km) at 15 knots
Complement:	14 officers 92 enlisted crew
Sensors and processing systems:	1 × HR-44D multipurpose radar Spherion hull sonar ŬG-4 anti-mine/diver sonar AN/SQR-19 towed array sonar
Electronic warfare & decoys:	1 × JJ-7 ESM antenna 1 × D-104 datalink 2 × Baram-2 countermeasure launchers 1 × Sebu towed torpedo decoy
Armament:	1 × HP-76/1 single 76mm turret 4 × YDH-26 anti-ship missile 1 × GBM-23/5 Dungji CIWS 2 × 2 400mm torpedo tube 2 × HBDJ-21/6 depth charge launcher 1 × HB-6/7 anti-frogman weapon 28 mines
Aircraft carried:	1 × GH-28 Ppulsoeori
Aviation facilities:	landing pad with hauldown winch hangar

The Mirun-class corvettes (Menghean: 밀운 중형 대잠수함 초계함 / 密雲級中型對潛水艦哨戒艦, Mirun-gŭb Junghyŏng Daejamsuham Chogyeham) are a group of oceangoing anti-submarine corvettes built for the Menghean Navy in the late 2000s and early 2010s. They are sometimes transliterated as the Milun class, and a few sources regard them as frigates due to their size and capabilities.

Although the Mirun-class and Sŏwicho-class are both labeled as corvettes in most foreign-language literature, and were built simultaneously with one another, the Menghean Navy regards them as "medium" and "small" anti-submarine patrol ships, respectively. Unlike the Sŏwichos, which are purely designed for coastal patrol duties, the Mirun-class vessels are able to conduct long-endurance patrols in the open ocean. They displace more than twice as much as their smaller cousins, and carry helicopter facilities and vertical launch boxes for the HŎ-3 Ryongorŭm standoff torpedo weapon. They also have better seakeeping capabilities and a longer at-sea endurance time.

Development

By the early 2000s, the Menghean Navy had a well-established convention of distinguishing between "anti-submarine patrol ships" (DChD, DChJ, and DChS types) and "escort ships" (HJ, H, and HW types). The latter types are designed as well-rounded escort ships able to protect an aircraft carrier or strike package from a variety of threats. Later HJ/H/HW designs are also capable of launching coordinated anti-ship missile strikes, a role borrowed from the Chŏndong-class and Nunbora-class "missile destroyers." "Anti-submarine patrol ships," by contrast, are highly specialized around the anti-submarine role, and are designed to autonomously patrol Menghean waters in search of enemy submarines or escort cargo ships in rear-area waters with less pronounced enemy air and surface threats but a high risk of incursion by submarines. The Mirun-class ships are designated in Menghe as "medium anti-submarine patrol ships," in between the Sŏwicho-class small ASW patrol ships which operate in coastal areas and the Chanjok Jachido-class large ASW patrol ships which lead their formations.

The Mirun-class were first conceived of as a replacement for the nine Mugunghwa-class corvettes which were refitted with towed array sonar for blue-water operations. Although this refit allowed the ships to detect targets below the thermocline, they suffered from poor seakeeping and limited endurance, two problems aggravated by the large tow structure built on top of the quarterdeck. Ten ships were ordered, to allow eight in a combat-ready state and two in major servicing at any given time. While the towed-array Mugunghwas were designated as DChS types, the new corvettes would be designated as larger DChJs, and would have helicopter facilities and anti-submarine missile launch cells. The first hull was laid down on 25 January 2005 at the Gyŏngsan Songsu-do Naval Yard.

Characteristics

Sensors

The Mirun-class ships carry relatively sophisticated sonar equipment. The hull sonar is a Glasic "Spherion" system, and is mounted in a sound-transparent dome under the keel just forward of the superstructure. This placement corrects a problem identified on the Hawŏn-class frigates, where the bow sonar - intended for larger ships - would break above the waterline in rough seas. The towed array sonar is an AN/SQR-19 array licensed from Hallia but built in Menghe. This system is identical to that carried by the larger Chanjok Jachidos and Haejus, and allows long-range detection of submarines operating below the thermocline.

Radar equipment, by contrast, is very minimal. The only air search radar carried is the HR-44D, carried on a solid mast above the bridge. This system has a range of only 40 kilometers against fighter-sized targets, and while it can detect higher-altitude targets than the baseline HR-44G, it is mainly intended to detect surface ships, periscopes, and sea-skimming missiles. It also doubles as a fire-control system for the ship's 76mm gun turret, though in continuous-illumination mode it must stop searching for other targets.

Armament

The ships' most unusual armament consists of a single 8-cell Mk 41 VLS module installed immediately aft of the funnel. This module uses strike-length cells with 6.7-meter-deep launch canisters, the largest type in use in Hallia, Tír Glas, and Dayashina, and along with its exhaust duct system it extends three decks into the hull, resting on top of the aft engine compartment. Given the Miruns' anti-submarine specialization, all eight cells would normally be loaded with HŎ-3 Ryongorŭm rocket-deployed torpedoes. In theory the ships could also be armed with cruise missiles or anti-ship missiles for a strike mission, though their weak air-defense armament would leave them vulnerable to attack in this role.

For closer-range engagements, the ships carry two twin 350mm torpedo tubes in pivoting launchers, one on each side. These are located behind folding covers which protect them from the elements and reduce radar reflection when not in use. Both legacy YŎ-35/1 and new YŎ-35/2 torpedoes are supported, with 12 stored in the magazine space forward of the hangar. Torpedoes from this magazine space can also be loaded onto the ship's helicopter.

Apart from the 76mm dual-purpose gun, the ships' sole anti-air armament consists of a single CIWS turret just forward of the helicopter hangar. This is sometimes incorrectly identified as a Subisu CIWS mount; in fact, it is a GBM-23/5Y Dungji, with a single 5-barrel rotary cannon and non-reloadable YDG-61 missile boxes. The mount's position gives it an excellent field of fire, leaving only a 20-degree gap in coverage directly forward. Captains of Mirun-class ships, like captains of Ginam-class ships, are instructed to turn away from the threat if they detect incoming missiles.

Basic anti-ship armament consists of two dual-cell angled launch boxes for YDH-26 anti-ship missiles. As on the Sŏwicho-class, these exist purely for self-defense, and use the lightest dedicated anti-ship missile in the Menghean arsenal.

Propulsion

The powerplant of the Mirun-class corvettes consists of a CODAG system linking a 30,000 shp (22,000 kW) LM2500 gas turbine to two Samsan S9000H 8,000 shp (5,965 kW) diesel engines. At full power, the ships can reach a top speed in excess of 30 knots, allowing them to outrun or keep pace with contemporary Anglian and Sieuxerrian nuclear submarines. A maximum range of 4,400 nautical miles (8,150 kilometers) also allows the Miruns to remain on patrol for a relatively long time, especially with at-sea refueling.

The individual parts of the powerplant are rail-mounted, and all components can be removed through the funnel for maintenance.

Countermeasures

As the Mirun-class corvettes are meant to locate, engage, and destroy enemy submarines, they incorporate a number of design features intended to improve their survivability against undersea threats. All engines, generators, and transmission parts in the Mirun class are mounted on acoustic damping mounts, which absorb vibration and reduce the ships' acoustic signature when operating at low speed. A diesel-electric or all-electric transmission was reportedly considered, as this would reduce vibration even further, but in the end all motor units were directly coupled to the propeller shafts.

For further noise reduction, the ships were fitted with a Prairie-Masker system to mask engine noise from within the hull and counteract cavitation around the propellers. They were among the first Menghean warships to be fitted with such a system.

On the first series of ships produced, there is a single HBDJ-21/6 anti-submarine rocket projector on each side of the helicopter hangar facing aft. These are exclusively used for the torpedo countermeasures role, firing either H-21ŎDG jamming rockets or H-21ŎDN anti-torpedo hardkill rockets. The launchers can be automatically trained, elevated, and fired from the ship's control room, but must be reloaded manually. Twelve reloads per launcher are carried, and are hoisted up from a storage room below deck.

Aircraft facilities

The Mirun-class corvettes are fitted with a landing pad and hangar for a single GH-28 Ppulsoeori. Some early design proposals used a smaller hangar for a navalized GH-30 or GH-34 helicopter, but in the end the GH-28 was deemed adequately compact. As on other oceangoing Menghean ships, the landing pad has a hauldown winch and taxi rail, allowing landing operations in rough seas.

Utility deck

In addition to the towed sonar array handling equipment and towed torpedo decoy, the enclosed deck underneath the helicopter landing pad also has reserved working space for other mission-specific equipment. The ships can be easily refitted to lay mines, including conformal mines, from rails in this working deck, and can also deploy remote-controlled mine-hunting unmanned undersea vehicles. They may be capable of deploying permanent acoustic surveillance devices onto the seabed. Some Menghean media sources claim that the aft utility deck can be used to house a special forces squad and its equipment, but the lack of dedicated boat launch facilities and the limited intersection with the ships' oceangoing anti-submarine role casts some doubt on this claim.

Ships in the class

In keeping with the precedent set by the Ginam class, the Mirun-class corvettes are all named after Menghean prefectures.

See also

• Chanjok Jachido-class cruiser (larger counterpart)
• Sŏwicho-class corvette (smaller counterpart)