Chanjok Jachido-class cruiser

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

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.

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.

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.