Ansa-class frigate

The Ansa-class frigates (Menghean: 安沙級外層護衛艦 / 안사급 위충 호위함, Ansa-gŭb wichung howiham) are a class of frigate designed and built in Menghe during the 1990s. Ten ships were produced in total, though the last four are sometimes considered a separate Hawŏn class due to modifications made during construction. They were the first postwar Menghean surface combatants to be built as general-purpose escort ships, with balanced anti-air, anti-ship, and anti-submarine capabilities.

Development

The Ansa-class frigates were conceived of as general-purpose, well-rounded escort ships, which would sit on the outer edge of a high-value formation or convoy to protect it from air and submarine attack. During the design process they were known as Plan 308. In particular, they were intended as escorts for the newly-built aircraft carrier Haebang, which entered service in 1990, and as general-purpose escorts for formations of landing ships.

The Yobu-class destroyer Maepo, completed to a modified design after the Decembrist Revolution, served as a conceptual testbed for a number of solutions implemented on the Ansa class. In particular, Maepo's surface-to-air missile armament consisting of two single-arm YDG-37 launchers was carried forward into the Ansa class.

Initially, Menghean designers hoped to use a combined diesel or gas powerplant, to balance sprint speed and cruising efficiency. Dayashina, however, blocked sales of the LM2500 turbine via Tír Glas and Hallia, still concerned that Menghe's new regime could turn hostile to Dayashinese interests. A domestic all-diesel powerplant was considered next, but preliminary studies found that it offered inadequate speed at full power. Eventually, Menghe purchased M7 combined gas turbine units from Letnia, each one consisting of two 6,000 hp M60 turbines for cruising and two 18,000hp M3 turbines for sprint operations in a COGAG arrangement.

Characteristics (as built)

Sensors

Ansa-class ships carry a single HR-240 radar on the main sensor mast. This is a Menghean licensed version of the Letnian MR-710 Fregat ("Top Plate") radar system, with two angled 3D arrays and an IFF antenna above them. Unlike the Chŏndong and Yobu classes, there is no second radar unit for multi-frequency capability or redundancy; the aft sensor mast sports a fire-control antenna instead.

For underwater search, the first six ships carry an MG-332T "Titan-2T" active/passive hull sonar and an MG-325 "Vega" towed variable-depth sonar. These are upgraded versions of the sonar equipment carried on the Ginam and Hyŏngnam class ships.

Armament

The Ansa-class ships' main surface-to-air armament consists of two 3S90 "Uragan" single-arm missile launchers licensed from Letnia. The missile's Menghean designation is YDG-37. Each mount sits atop a magazine with 24 missiles, and takes 12 seconds to complete a full reloading cycle. The missile has a range of 30 kilometers. Each ship has four 3R90 illumination radars to guide these missiles, with two on each side of the superstructure.

Close-range air defense consists of two GBM-30/6 CIWS mounts, Menghe's licensed copy of the AK-630. These are arranged with one mount on each corner of the superstructure. There are only two corresponding MR-123 fire-control radars, each linked to two mounts, so the CIWS battery can only engage two targets at once - and in most directions, only with one gun at a time. The 100mm gun turret on the foredeck also has anti-air and anti-missile capability.

Anti-submarine armament, shared with the Ginam, Hyŏngnam, and Chanjok Jachido classes, consists of two quadruple 533mm torpedo tube mounts, one on either side. The corresponding deck of the superstructure is partially cut away to allow these mounts to traverse. In addition to wire-guided homing torpedoes, these mounts can also launch the HŎ-2 Poksŏl anti-submarine standoff weapon. For close-range anti-submarine attacks, the ships also carry two RBU-6000 depth charge rocket projectors on the foredeck.

During construction of the first two ships, the design was modified to fit angled launch boxes for the YDH-24 anti-ship missile, which was still in development. Ansa was commissioned without AShM boxes; Wisin, Tongjin, and Gokhap were commissioned with a pair of two-missile boxes. During regular minor maintenance stops, all ships in the class were eventually fitted with twin and later quadruple launchers for the YDH-24.

Aircraft facilities

All Ansa-class ships are built with a landing pad and hangar for a GH-28 anti-submarine helicopter. Unlike the Ginam and Hyŏngnam classes, in which the hangar is recessed one deck into the hull with a partially sloped floor, the hangar on the Ansa class is at the same level as the landing pad. The landing pad also incorporates a hauldown winch which can assist in rough-weather landing operations and tow the recovered helicopter safely into the hangar.

Even with these changes, however, crews still complained that the hangar was relatively narrow, making repair and re-arming difficult. Multiple ships would also have to work together to keep one helicopter on station at all times between them.

Hawŏn subclass

While Hallia was unable to sell any equipment containing Glasic or Dayashinese parts to Menghe, it did export three advanced sonar suites in the early 1990s, for use on the Chanjok Jachido-class cruisers. When the lead ship of this class conducted at-sea trials and exercises in 1994 and 1995, both her bow-mounted sonar and towed sonar array were found to have vastly superior performance to the systems installed on the recently-completed Ansa. Menghe responded by signing a contract for eight additional Hallian sonar sets. Four of these would be used for the Pyŏng'an-class destroyers, which were still in the design phase; the other four would be mounted on future Ansa-class frigates, modified to make the best use of the new systems.

The first Ansa-class frigate to be completed with the new sonar arrangement was Hawŏn, commissioned in 2000. As such, in Menghe and abroad, the modified frigate design is sometimes known as the Hawŏn class. Externally, the Hawŏn-class ships are nearly identical to the first six units in the class, differing mainly in a slight extension to the quarterdeck. Internally, however, the aft sonar handling rooms follow an entirely different layout, as they are designed to carry a towed array rather than a bulky sonar unit at the end of a cable. The sonar bulge under the bow was also modified.

Refits and upgrades

While Ansa was commissioned without anti-ship missile armament, she was spotted in 1994 with two twin YDH-24 launch boxes mounted in the space between the bridge and the funnel. These were likely added during a routine maintenance check, and it is likely that Ansa was completed with the mounting locks for the launchers already in place.