Yobu-class destroyer

Yobu class

H Yobu as she appeared in 1979.
Class overview
Name:	Yobu class
Builders:	Gyŏngsan Songsu-do Naval Yard
Operators:	Menghe
Preceded by:	none
Built:	1974-1992
In service:	1978-present
Planned:	17
Completed:	14
Cancelled:	3
General characteristics Yobu-class, as built
Type:	Guided missile destroyer
Displacement:	4,400 tonnes standard 5,200 tonnes full load
Length:	140.2 m (waterline) 147.8 m (overall)
Beam:	16.1 m
Draft:	4.58 m
Propulsion:	2-shaft steam turbine 4 boilers 2 steam turbines (40,000 shp each)
Speed:	32 knots
Range:	5,500 nautical miles (10,000 km)
Complement:	297
Armament:	2 × YDG-32 twin-arm launcher (32 reloads) 2 × AK-762 dual 76mm turret 4 × AK-630 CIWS 2 × RBU-6000 depth charge projector 2 × 4 533mm torpedo tube 80 mines

The Yobu-class destroyers (Menghean: 요부급 호위함 / 饒富級護衛艦 Yobu-gŭb Howiham) are a class of warship built in the Democratic People's Republic of Menghe between 1974 and 1992. They are generally known in the West as guided missile destroyers, but in Menghe they are officially classified as "guard ships." Though similar in capabilities to the Letnian Kashin-class destroyers, the Yobu-class are an indigenous Menghean design, albeit one armed with licensed Letnian weaponry.

A total of 14 hulls were completed between 1978 and 1992, out of 17 ships ordered. Hulls 8 through 14, starting with Hyŏngnam, were built to a modified design with rearranged armament and a stretched stern, and are sometimes considered a separate ship class. The 14th ship, Maepo, was laid down as part of the Hyŏngnam subclass but completed with a different missile armament and sensor arrangement, and is sometimes considered a unique ship class.

Development

During the postwar emergency shipbuilding program, the DPRM laid down a large number of Taepung-class deestroyers and Nunbora-class destroyers. Simple designs optimized for mass production from Menghe's technologically delayed shipbuilding sector, these warships were oriented toward surface warfare, and relied entirely on dual-purpose guns and small-caliber AA guns for their anti-aircraft armament. This left them seriously vulnerable to enemy jet aircraft carrying anti-ship missiles.

Menghean engineers responded by developing a speial-purpose warship with more advanced anti-air and anti-submarine armament. To achieve the required characteristics on a small hull, they omitted anti-ship missiles, and reduced the gun armament to two 76mm twin turrets aft. The resulting design was also larger and more expensive than Menghe's contemporary destroyer classes. Together, these characteristics made it unsuitable as a full-on replacement. As such, the type was classified as a "guard ship" (howiham) tasked with escorting formations of destroyers (guchugham) that specialized in anti-surface warfare. This duality of destroyer types would persist in Menghean ship design philosophy until the middle of the 1990s.

The final blueprint was designated Plan 567. Its armament, radar, and sonar systems were all licensed from Letnia, but the hull was a domestic design, and it went through several redesign iterations. The first ship in the class, Yobu, was laid down on June 24th, 1974 in Drydock 1 of the Songsu-do Naval Base. Despite an initial requirement to keep length under 135 meters, the class ended up being too large for Songsu-do's small destroyer drydocks, and they were built in the cruiser-size drydock instead.

Design

In terms of their overall capabilities, the Yobu-class destroyers are similar to Letnia's Kashin-class destroyers, and they use many of the same weapon systems and sensors. Nevertheless, the Yobu-class can be easily distinguished by their aft superfiring guns, their single funnel with "solid" radar mast attached, and their wide bridge structure. Their 533mm torpedo armament is also split between two four-tube launchers, one on either side.

The ships' main anti-air armament consists of two twin-arm launchers for the YDG-32 surface-to-air missile, a licensed copy of the Letnian S-125 Neva/Pechora. The twin-arm launchers are also licensed copies of the Letnian ZIF-101 system, with 16 reload missiles per launcher in eight-missile carousels. For close-range air defense, the Yobu-class carries four AK-630 CIWS turrets, with each pair controlled by a single "Vympel" targeting radar with manual backup sight. Additionally, the ships' 76mm AK-726 turrets are dual-purpose weapons which can engage aircraft and missiles as well as surface targets. Air-search radar consists of one "Kliver" 2D search radar and one "Angara-A" search radar with height-finding capability.

Anti-submarine armament consists of two RBU-6000 rocket projectors forward, which can also fire torpedo decoy countermeasure rounds. The 533mm torpedo tubes on either side can launch both wireless homing and wire-guided torpedoes. The main sonar module, license-produced from Letnia, contains "Titan" and "Vychegda" sonar antennas, and can retract almost fully inside of the hull to aid in drydocking and shallow-water berthing. The original seveen Yobu-class ships lack variable-depth sonar.

The ships' powerplant is domestic in design, and consists of four high-pressure boilers connected to two steam turbines. Both the boilers and turbines use a domestic Menghean design. At full power, the ships can reportedly reach a top speed of 33 knots, but they lack the fast acceleration of gas-turbine ships. Exhaust from the turbines is vented through a single trunked funnel.

Variants and subclasses

Hyŏngnam subclass

The first of the Hyŏngnam-class destroyers as commissioned.

The original procurement plan called for twelve Yobu-class destroyers, to be laid down at a rate of one per year. As time passed, however, some shortcomings of the Yobu-class became apparent, most notably its lack of helicopter facilities. Initially, this was considered an acceptable tradeoff, as the Menghean People's Navy mainly operated close to shore; but by the middle of the 1970s, the Menghean leadership had growing ambitions for long-range patrol capability. In 1975, the DPRM began work on a tandem-rotor helicopter for shipborne use, later designated GH-28. With the type nearing operational readiness by 1980, the Navy leadership ordered a redesign of future Yobu-class hulls to support a helicopter for prolonged at-sea operations. Navy leaders also demanded the addition of a variable-depth sonar, a feature absent on the existing hulls.

In mid-1979, the remaining 5 planned Yobu-class ships were cancelled and replaced by 5 units the new guard ship design. This design, designated Plan 5672, added a variable-depth sonar under the quarterdeck, with a helicopter landing pad and hangar forward of it. In keeping with Letnian ship design practices, the hangar was recessed one deck, with a ramp leading into it and a sliding roof on top. These changes required extending the quarterdeck aft by 1.5 meters.

To make room for the hangar, the aft twin 76mm turrets had to be deleted. As a replacement, a single twin 76mm turret was added on the foredeck in place of the RBU-6000 anti-submarine rocket launchers, which were instead mounted on either side of the hangar. The relocation of the 76mm turret's fire-control radar to a forward-facing position led to a thorough redesign of the bridge and lattice mast. Additional deckhouse structures were added to the aft superstructure, apparently as accommodations for displaced crew accommodations.

The first ship built to this revised design, Hyŏngnam, was laid down on February 9th, 1980, and completed on November 6th, 1983. Western intelligence sources classified the ship as a subclass of the Yobu type, though in Menghe it was regarded as a separate ship class entirely. The next five hulls, including Hyŏngnam, were laid down according to schedule, and at the end of 1984 the DPRM budgeted five more as part of an emergency plan to strengthen the Navy in response to escalating tensions surrounding Menghe's nuclear weapons program. Two of these additional ships were laid down, and the remaining three were cancelled in 1988 following the Decembrist Revolution.

Maepo subclass

The Maepo as she appeared when commissioned. Permanent hull numbers were only assigned in 1994.

The destroyer Maepo, later assigned the permanent hull number H-313, was originally laid down as a standard Hyŏngnam-class design. At the time of the Decembrist Revolution, she was still in the early stages of construction, with building work stalled due to economic issues. Rather than scrap what existed of her hull, the Menghean Navy decided to continue work on her, but delayed the resumption of construction work. During this time, Menghe secured permission to import the 3S90 Shtil surface-to-air missile system from Letnia, and the Menghean Navy's engineers decided to convert the in-progress hull to serve as a testbed for the new system. The magazine of the 3S90 single-arm launcher is smaller than the magazine for the twin-arm YDG-32 missile launcher, making the conversion relatively straightforward, and the superstructure had not yet been built, allowing the designers to alter it to support new missile guidance systems. Construction was repeatedly delayed to allow time for design work, but Maepo was launched at the end of 1989 and commissioned in 1992.

Although it carries fewer surface-to-air missiles in ready-to-fire positions, the Maepo actually carries more surface-to-air missiles in total, with 24 rather than 16 per launcher. The YDG-37 missile is roughly comparable in range to the YDG-32 used by the other ships, but uses semi-active radar homing rather than radio command guidance and has somewhat better accuracy and performance, especially before Menghe implemented YDG-32 upgrades in the late 1990s. With four radar illuminators rather than two and a more advanced target handling system, the Maepo can also engage more targets simultaneously.

Mid-life refits

In 2002, shortly after acquiring a production license for the SM-2 missile, the Menghean Navy initiated a design study for an intensive mid-life refit which would equip some or all of the Yobu-class destroyers with the Mk 41 VLS. As the SM-2 used a different guidance system from the YDH-32, these refits would also require replacement of the guidance radars and onboard computers. To make the most of what would already be a major refit, the Navy also added requirements for more advanced air-search radars and a new sonar antenna and towed sonar array. In their new configuration, the ships would be suitable for another 20 years of service, at which point they would be retired. Due to cost and drydock space constraints, the Navy decided early on that these changes would only be applied to the six ships of the Hyŏngnam subclass, excluding the unique ship Maepo.

A preliminary engineering survey of the six Hyŏngnams, carried out between 2003 and 2004, forced the Navy to revise its refit plan. Inspectors found evidence of "significant cracking and structural strain" on all six ships, particularly around the forward YDG-32 magazine and the helicopter hangar. The Navy's engineers attributed the problems to three main faults: the high stresses created by the divergence of decks around the magazine in the base Yobu hull; the added weight of the forward turret and aft hangar and equipment in the Hyŏngnam subclass; and the use of steel of dubious quality, particularly in the mid-1980s when economic strain peaked.

The inspectors' final report concluded that the six Hyŏngnams were safe for another 10 years of service, but not for the 20+ years planned for a mid-life refit. Additionally, the report warned against any refits which would seriously alter the weight distribution or require extensive cutting and replacement of metal. Combined with the escalation of the Ummayan Civil War, which allowed the Navy to double its new-ship procurement plan, these assessments pointed to the conclusion that a comprehensive refit of the Hyŏngnams was not worthwhile.

Instead, the Menghean Navy opted for a more modest string of updates, to keep the ships relevant for the remaining 10 years of their service lives. The main change was to add compatibility with a newer model of YDG-32 missile, featuring extended range, greater accuracy, and greater resistance to countermeasures. The guidange radars and their supporting electronics were also updated in accordance with the missile's requirements. Amidships, the Navy also added two quadruple lauchers for lightweight YDH-26 anti-ship missiles, improving the ships' self-defense capability.

Ships in the class

A total of 14 destroyers in the broader Yobu family were laid down between 1974 and 1986. Of these, seven were of the basic Yobu class, six were of the Hyŏngnam subclass, and one (Maepo) was built to a unique configuration. All fourteen hulls were built at the Gyŏngsan Songsu-do Naval Yard, part of the Songsu-do Naval Base; they were built in Drydocks 1 and 2, the northernmost in the yard, due to their cruiser-like size.

In contrast to the Taepung, Nunbora, and Chŏndong classes, the Yobu and Hyŏngnam-class vessels were named after Menghean prefectures. This is because while the former three were domestically classified as "destroyers" or "missile destroyers," the latter were classified as "guard ships," a separate category. Interestingly, the Greater Menghean Empire also named its destroyers after prefectures of below-city rank.

Name	Mengja	Builder	Laid down	Launched	Commissioned	Status
Yobu-class escort ships
Yobu	饒富	Gyŏngsan	1974 06 24	1975 10 25	1978 12 23	--
Yŏngdong	永同	Gyŏngsan	1975 08 10	1977 01 14	1980 03 06	--
Rimjŏng	臨庭	Gyŏngsan	1976 01 25	1977 07 18	1980 03 07	--
Gahwa	嘉和	Gyŏngsan	1977 02 07	1978 09 27	1981 08 08	--
Gangju	絳州	Gyŏngsan	1977 08 09	1979 02 11	1981 02 16	--
Daehap	大峽	Gyŏngsan	1978 10 03	1980 01 24	1982 11 12	--
Gŏchang	居昌	Gyŏngsan	1979 03 01	1980 09 29	1983 06 27	--
Hyŏngnam-class escort ships
Hyŏngnam	營南	Gyŏngsan	1980 02 09	1981 07 14	1983 11 06	--
Migi	尾崎	Gyŏngsan	1980 10 15	1982 04 01	1984 08 26	--
Wŏlju	袁州	Gyŏngsan	1981 07 22	1983 01 26	1985 05 25	--
Pogok	蒲谷	Gyŏngsan	1982 04 12	1983 09 06	1986 03 15	--
Yŏnju	兗州	Gyŏngsan	1983 09 14	1985 03 21	1988 03 07	--
Muju	茂朱	Gyŏngsan	1985 03 31	1986 10 05	1989 08 10	--
Maepo-class escort ship
Maepo	梅浦	Gyŏngsan	1986 10 12	1989 11 29	1992 06 02	--