Chanjok Jachido-class cruiser

Chanjok Jachido class

3-view image of Chanjok Jachido as built
Class overview
Name:	Chanjok Jachido class
Builders:	Gyŏngsan Songsu-do Naval Yard
Operators:	Menghe
Preceded by:	none
Built:	1991-1997
In service:	1994-present
Planned:	3
Completed:	3
General characteristics Chanjok Jachido, as built
Type:	Helicopter cruiser
Displacement:	7,200 tonnes standard 8,600 tonnes full load
Length:	153.9 m (waterline) 164.5 m (overall)
Beam:	18.4 m (waterline)
Draft:	6.09 m (to keel)
Propulsion:	2-shaft steam turbine 4 boilers 2 steam turbines (50,000 shp each)
Speed:	30 knots
Range:	6,000 nautical miles (11,000 km) at 14 knots
Complement:	47 officers 391 enlisted
Armament:	2 × 3S90 single-arm launcher (32 reloads) 2 × 4 YDH-24 anti-ship missile 1 × AK-176 single 76mm turret 2 × AK-630 CIWS 2 × RBU-6000 depth charge projector 2 × 4 533mm torpedo tube 4 × HBDJ-6/7 anti-frogman weapon

The Chanjok Jachido-class are a group of three large warships built for the Menghean Navy in the 1990s. While anglian sources usually refer to them as cruisers or helicopter cruisers due to their large size and command facilities, in Menghe they are officially classified as Large Anti-Submarine Patrol Ships (대형 대잠수함 초계함 / 大型對潛水艦哨戒艦, Daehyŏng Daejamsuham Chogyeham). As the name suggests, they are designed to lead surface action groups on anti-submarine patrols, and for this purpose they come equipped with advanced sonar equipment and a hangar supporting four GH-28 helicopters. All three ships received major refits in the 2010s, and all remain in active service as of 2020.

Development

The Democratic People's Republic of Menghe solicited several designs for an oceangoing anti-submarine flagship during the 1980s, including one with standoff rockets carrying nuclear depth charges. Large helicopter facilities were common to most of these designs, as the Ginam-class frigates only carried a single helicopter each. Due to the economic instability under Ryŏ Ho-jun and the Emergency Shipbuilding Program's focus on anti-surface combatants, these designs never came to fruition. Following Choe Sŭng-min's Decembrist Revolution, however, the opportunity to build a new anti-submarine warship returned, especially after the completion of the aircraft carrier Haebang freed up more funds for construction.

As with the contemporary Ansa-class frigates, Menghe tried to take advantage of the improved diplomatic situation by seeking foreign sellers for the ship's electronics and powerplant. Tír Glas blocked the sale of LM2500 gas turbines due to objections from Dayashina, leaving Menghe with no option but to modify the design for a domestic steam turbine powerplant - making her the last Menghean warship class to use a powerplant of this type. Hallia, however, agreed to provide an advanced sonar suite consisting of the AN/SQS-53B hull-mounted sonar and AN/SQR-19 towed array sonar, as part of an effort to limit EC influence in the South Menghe Sea.

The resulting design was given the project designation Plan 435. This was the final iteration of the design, with a revised deck layout and superfiring surface-to-air missile mounts. The first ship in the class was laid down on February 7th, 1991, at Drydock 1 of the Gyŏngsan Songsu-do shipyard.

Characteristics (as built)

Sensors and electronics

The centerpiece of the Chanjok Jachido's anti-submarine capability is its imported Hallian sonar suite. This consists of the AN/SQS-53B hull-mounted sonar and the AN/SQR-19 towed array sonar, two state-of-the-art Hallian systems. While some Mugunghwa-class corvettes were modified with experimental towed sonar systems, Chanjok Jachido was the first ship to carry an operational towed array sonar. Trials and exercises demonstrated that the AN/SQR-19 was, in one naval officer's words, "orders of magnitude superior" to the Letnian-designed MG-325 "Vega" on the Ansa-class frigates, prompting a modification of later Ansa hulls.

For air-search equipment, the Chanjok Jachido carries an MR-710M Fregat-M (Top Steer) D-band radar on a mast aft of the bridge. This is paired with two guidance radars for the 3S90 SAM system, both atop the bridge. Although this is half as many guidance radars as the smaller Ansa class, their positioning gives them wider 300-degree targeting arcs.

The ships' electronic warfare suite, consistent with other Menghean surface combatants of this period, consists of two passive ESM surveillance and classification antennas and four active ESM jamming antennas, all on the main radar mast.

Armament

Anti-submarine armament consists of two quadruple 533mm torpedo tubes, one on each side of the hull. They are located inside the superstructure, behind retractable panels which cover them when they are not in use. In addition to wire-guided torpedoes with active sonar, these mounts can fire the HŎ-2 Poksŏl anti-submarine weapon, which launches out of the water on a ballistic trajectory and carries a smaller homing torpedo to the target. Uniquely for a Menghean postwar warship, the mounts are reloadable: a total of 8 torpedo reloads are carried, usually a mix of wire-guided homing torpedoes and HŎ-2s.

Additionally, ships in the class carry two HBDJ-21/12 anti-submarine rocket launchers on the foredeck. Due to their short range, these are mainly used to deploy sonar decoys and, on later models, anti-torpedo hardkill countermeasures.

Air-defense armament consists of two 3S90 Uragan single-arm SAM launchers, in a superfiring arrangement forward of the bridge. While a twin-arm launcher would have been superior, the 3S90 mounts were purchased as off-the-shelf systems from Letnia, and installed in their present form. For short-range anti-missile defense, the ships carry two AK-630 close-in weapon systems. Both are aimed by a single MR-123 radar director with manual backup, meaning that the ship can only engage one missile threat at a time. Additionally, the surface-to-air missile systems are unable to engage threats to a 60-degree arc over the rear, and the AK-630 mounts are unable to engage threats over a 60-degree arc forward (they have overlapping coverage aft). These tradeoffs were considered acceptable for a warship which is mainly intended to conduct anti-submarine patrols in areas with a low enemy aircraft threat.

The Chanjok Jachidos have their AK-176 dual-purpose guns in an unusual amidships arrangement, giving each mount a roughly 160-degree firing arc. These mounts are capable of engaging aircraft and missiles, and have a maximum range of 15.5 kilometers against surface targets, with an effective range of 10 kilometers. These are also directed by MR-123 radar units, located above the bridge facing aft.

As designed, these ships did not carry anti-ship missiles, as their anti-submarine patrol role did not require it. During the fitting-out process, however, they were modified with four quadruple launch boxes for YDH-24 subsonic anti-ship missiles. Mounting atop the hangar structure was initially considered, but the missile boxes were moved to a position forward of the funnel due to concerns about the hangar structure's bracing being inadequate.

Propulsion

Cross section of Chanjok Jachido as built, showing the steam turbine power plant and extensive command spaces.

The Chanjok Jachidos were the last Menghean warships to be built with steam turbine propulsion rather than a more modern engine system. Each shaft is powered by a single 50,000-shp turbine, with steam provided by four advanced high-pressure boilers. The original design made poor use of acousting damping, and vibration from the engines was easily detected on passive sonar, undercutting the ships' anti-submarine role.

Command facilities

Owing to their role as flagships for anti-submarine fleets, Chanjok Jachido class cruisers have generous command facilities on board. Unlike the small command room on the Yobu-class destroyers, which serve as destroyer leaders for a brigade of 2-4 other ships, the command facilities on the Chanjok Jachidos are intended to support command and coordination of up to a dozen warships of different types under the command of a three-star vice admiral. The command room is located inside the hull of the ship, one deck above the combat information center, and includes facilities for communication and air traffic control.

Because of their onboard flag facilities, in addition to their large size, these ships are classified as cruisers by the Glasic, Dayashinese, and Hallian navies.

Aviation facilities

The ships' main anti-submarine capability comes from their aviation facilities. The large aft hangar structure can support four GH-28 helicopters, compared with one at most on all contemporary Menghean warships. The hangar itself is also more spacious, especially compared to the hangars on the Hyŏngnam-class destroyers and Ginam-class frigates, which include sloping floors and narrow walls to reduce the hangar's external footprint. As a result, servicing and reloading of helicopters is easier to carry out.

Aft of the hangar is a large helipad. The ships were originally intended to have two helicopter landing positions, but design evaluations concluded that a single landing position with two open-air servicing positions forward would result in faster turnaround times, preferable in anti-submarine operations. The single aft landing position is fitted with a hauldown winch to allow recovery of helicopters in heavy seas. A towing system can move anchored helicopters to either on-deck servicing area, but from there they must be rolled into the hangar manually.

After refits

During the early 2010s, all three ships underwent major rebuilding as part of their mid-life refits. The goal of the refits was to extend the ships' service lives by fitting them with state-of-the-art machinery and weaponry. Compared with other mid-life refits in the Menghean Navy, the changes were relatively comprehensive, and in some respects amounted to a full rebuild.

Propulsion

The most thorough changes concerned the ships' powerplant, which was already noisy and inefficient by the standards of the 1990s - a poor combination for an anti-submarine patrol ship. To correct this problem, the entire steam powerplant was torn out, a process which required cutting away large sections of the hangar and superstructure. This was the most expensive and time-consuming part of the refit process.

In place of the old powerplant, the shipyard installed a new IEP system using a combined-gas-electric-and-gas (COGLAG) arrangement. To preserve the arrangement of the propeller shafts, brushless electric motors were installed in place of the steam turbines, and four LM2500 gas turbines connected to electric generators were installed in place of the boilers. This resulted in two engine rooms, each containing one shaft and two turbine-generator sets. The backup diesel generators were also replaced with newer, more efficient models, which could supply the propulsion systems as well.

All components in the new powerplant were mounted on top of acoustic damping supports. In addition to the use of precisely engineered electric motors for the final transmission stage, this greatly reduced the ships' acoustic signature, especially while operating on reduced power. These damping supports also included rails, allowing individual pieces of machinery to be moved to the central compartment and lifted up through the funnel for easier maintenance. While the refits were initially intended to keep the ships effective in combat for the next 20 years, a Navy evaluation of improved maintenance options concluded that this could be extended to as long as 30 years through regular replacement of powerplant elements and electronics.

Plan 351 Yerihan derivative

Cross-section drawing of the Plan 351 design.

Plan 351 Yerihan ("Keen") was a cruiser design (officially classified as "main force escort" or juryŏk howiham) derived from the Chanjok Jachido class. The design was drawn up during the mid-1990s, and was intended as a fleet escort for the Chanjok Jachidos themselves and the Menghean aircraft carrier Haebang. It retained the hullform, powerplant, bridge, and forward armament of the Chanjok Jachido class, but replaced the helicopter hangar with eight 8-tube rotary launchers for the YDG-39 (Rif-M) surface-to-air missile. This gave it a powerful 64-missile long-range anti-air armament, compared to 54 missiles on the Pyŏng'an class, in addition to the forward-facing single-arm launchers.

The Plan 351 design also modified the layout of the boiler exhaust, which no longer had to be trunked together forward of the funnel. Instead, the ship would have been built with two large pyramid-like towers, each combining an exhaust vent and an air-search radar array with electronic warfare equipment along the sides. Because the boilers were arranged asymmetrically, the forward exhaust was offset to port, and the aft exhaust was offset to starboard. The main radar array was a Letnian Podberezovik-ET1, Menghean designation HR-300, later used on the Pyŏng'an class.

While mainly intended as wide-area anti-aircraft escorts, the Plan 351 ships retained most of the Chanjok Jachidos' anti-submarine capability. The hull and towed sonar were identical, and even with the large missile farm aft, the design had room for one helipad and two GH-28 helicopters. The torpedo tubes were moved slightly aft, with an improved onboard reloading system.

On paper, the Plan 351 design was superior to the competing Plan 332, which became the Pyŏng'an class. It offered a larger long-range missile magazine, better medium-range missile defenses, a superior air-search radar arrangement, and the advantages of a proven hull. It also retained the fleet command facilities of the Chanjok Jachido, and would almost certainly have been classified as a cruiser abroad if built. Choe Sŭng-min personally endorsed the design. Nevertheless, Navy administrative staff determined that the same budget would only support three of these ships, compared to five units of the Plan 332 design, which would allow more dispersed air-defense coverage. Detailed design work on Plan 351 also uncovered serious structural problems due to the added weight on the aft section and the bulkier pyramid masts. The last round of designs place full load displacement at slightly over 10,000 tons, after accounting for additional structural supports. In the end, the Ministry of National Defense selected the competing Plan 332 design, which went on to become the Pyŏng'an-class destroyer.

Role in reclassification of ships

Prior to the introduction of the Chanjok Jachido class, the hull type DChD (Large Anti-Submarine Patrol Ship) was assigned to the Ginam-class frigates, which had helicopter hangars and division command facilities. Because the Chanjok Jachidos were so much larger and more capable, the Menghean Navy decided to reclassify all of its anti-submarine warships to reflect their new distribution.

Under the updated classification scheme, the Chanjok Jachidos remained Large Anti-Submarine Patrol Ships; the Ginams were reclassified as Medium Anti-Submarine Patrol Ships; the Mugunghwas were reclassified as Small Anti-Submarine Patrol Ships; and the previous classes of Small Anti-Submarine Patrol Ship were retired from service, having long ago become obsolete.

Ships in the class

A total of three Chanjok Jachido-class cruisers were completed. All are named after Menghean Semi-Autonomous Provinces (자치도 / 自治道, jachido), specifically the SAPs of the Chan (Argentan), Rak (Lac), and Kungnae (Kungnai) minorities. No other Menghean warships have been named for province-level divisions.

Name	Mengja	Builder	Laid down	Launched	Commissioned	Status
Chanjok Jachido	儧族自治道	Gyŏngsan	1991 Feb 02	1992 Dec 25	1994 Mar 16	In service
Ragjok Jachido	駱族自治道	Gyŏngsan	1993 Jan 13	1994 Nov 14	1996 Jan 02	In service
Gwangnaejok Jachido	廣內自治道	Gyŏngsan	1994 Nov 28	1996 Aug 22	1997 Sep 16	In service