Hasŏ-class cruiser

The Hasŏ-class cruisers are a group of four large helicopter carriers in service with the Menghean Navy. They are formally designated as "large anti-submarine patrol ships" (Menghean: 대형 대잠수함 초계함 / 大型對潛水艦哨戒艦, Daehyŏng Daejamsuham Chogyeham), but in Anglian language literature they are typically referred to as cruisers or helicopter carriers due to their large air wing. They specialize in the anti-submarine role, with an advanced hull sonar and variable-depth sonar, and are also armed for self-defense against submarine-launched anti-ship missiles.

Development

After the Innominadan Crisis, the Entente Cordiale began basing nuclear guided missile submarines in Maracaibo, eliminating the need to transit through the Strait of Portcullia en route from bases in Solevant or West Khalistan. This created a serious challenge for Menghe, as Maracaibo's long coastline would allow SSGNs to approach Menghe anywhere over a wide area, with no choke points in between. Furthermore, Menghean intelligence assessments indicated that the EC was developing a submarine-launched cruise missile with a range of 2,500 kilometers, which would greatly expand the area of the "launch box" from which SSGNs could hit naval installations in Quẚng Phẚ and Songsu-do.

Both of these developments meant that the former strategy of sending an anti-submarine warfare group to patrol the SSGN launch box itself was no longer viable; the Ministry of National Defense demanded that the Navy prevent SSGNs from entering the launch box in the first place, or at least detect them en route and dispatch hunter-killer submarines to shadow them. Setting up a detection cordon between the launch box and Maracaibo would require that the Navy patrol a much wider area of ocean with a greater density of surface ships.

The Hasŏ-class cruisers were developed in response to this requirement. In development, they were known as the DChD-06 class, after the hull number that would be assigned to the first ship in the series. A wide variety of proposals were considered, including a flight deck conversion of the planned Insŏng-class destroyer and a light aircraft carrier with a single catapult for launching DY-11 anti-submarine patrol aircraft.

One of the associated requirements of the project was that it be able to send patrol aircraft over a wide area. Navy design staff concluded that the existing GH-28 had inadequate range for this role, but attempts to carry fixed-wing patrol aicraft like the DY-11 required an excessively large hull and flight deck. Consequently, the Navy issued a design requirement for a compound helicopter capable of deploying sonobuoys over a wide area. This requirement led to the development of the Gyundoan-Han GH-36 Mulsuri, which was designed in tandem with the DChD-06 projects.

In 2015, the Menghean Navy settled on the final design for the DChD-06 anti-submarine patrol ship. The first ship in the class, Hasŏ, was laid down on 17 February 2016 at the Gyŏngsan Songsu-do Shipyard. To expedite her construction, the Navy cancelled the four remaining Hwangtaesan-class amphibious transport docks of the original twelve-ship order, which would have been built in the same drydocks.

Design

Layout

The most distinctive feature of the Hasŏ-class cruisers, and the main reason for their popular classification as cruisers rather than carriers, is their unconventional layout. Rather than a full flight deck alongside an island, they are built with small flight decks forward and aft and a large superstructure in between. This superstructure contains both of the ship's elevators, as well as a "tunnel" connecting the fore and aft flight decks. This arrangement was chosen to increase the number of helicopters that could be stored without parking any on deck, and to better protect the elevators from the elements. These changes would allow for safer operations in heavy seas, important when patrolling an area known for its typhoons.

Overlooking the forward flight deck are two large rows of windows. The upper level contains the navigation bridge used for steering the ship. The level below it contains the air traffic control stations for the forward flight deck. The air traffic control stations for the aft flight deck are positioned in a separate overlooking station aft.

The combat information center is located within the hull, forward of the hangar, for greater protection. In addition to planning the ship's own operations, this command center is also used to coordinate the operation of a larger anti-submarine battle group. These substantial command facilities are the other main reason for the tendency of other navies to classify the Hasŏs as cruisers.

On either side of the superstructure stand two large hoist towers with fuel and water hoses, used for underway replenishment. This equipment allows the Hasŏ-class ships to replenish the fuel tanks of smaller ships in the formation, especially Mirun and Yungju-class corvettes, extending their endurance if they have burned excess fuel chasing a possible sonar contact. Solid-cargo transfer equipment was considered on some iterations of the design, but ultimately omitted due to the space it would have required. There are, however, two solid-cargo receiving kingposts, and four receiving ports for fuel and potable water.

Air wing

A typical air wing for a Hasŏ-class cruiser consists of:

• 12 × GH-36N anti-submarine compound helicopter
• 3 × GH-28B airborne early warning helicopter
• 3 × GH-28D airborne search-and-rescue helicopter

Five helicopters can be stored in the deck-level hangar, and thirteen can be stored in the internal hangar. Two elevators lift helicopters between the internal hangar and the deck-level hangar. When a sufficient number of the ship's helicopters are away, the tunnel inside the hangar can also be used to move aircraft between the forward and aft landing areas. Both the deck-level hangar and the internal hangar can be divided in two by a fireproof partition.

There are two flight decks for helicopter operation: one forward of the superstructure, and one aft. The aft flight deck has two takeoff and landing positions, staggered diagonally. This arrangement allows one helicopter to land at the aft-most (No.3) landing position if the No.2 landing position is occupied. The forward flight deck has a single takeoff and landing position, located well forward of the superstructure to allow helicopters to make a safe landing approach from a 45-degree bearing off the port or starboard side.

During development, the Menghean Navy considered modifying the design to allow launch and recovery of VTOL or V/STOL fighters, with a ski jump forward and heat-resistant flight deck coating. In the end, this configuration was not chosen, as Menghe had no prior experience designing or operating V/STOL fixed-wing aircraft and the addition of any fighter aircraft to the air wing would require the removal of more important GH-36 airframes. Press releases by the Menghean Navy, however, have stated that the Hasŏ class can be modified in mid-life refits to operate future V/STOL fighter aircraft if necessary.

Sensors

The sonar suite aboard the Hasŏ-class cruisers is the most advanced type carried by any Menghean warship class, apart from the Plan 1850 ocean surveillance ships. The hull sonar is a powerful low-frequency active/passive unit with large side-facing arrays, built under license from Tír Glas. The aft sonar equipment consists of a Ŭ-100D large variable-depth sonar with active and passive modes on the port side, and an AN/SQR-19 towed array sonar on the starboard side. These two systems can be used in conjunction for improved detection capability.

The radar suite consists of a SMART-L long-range search radar for detecting and tracking aircraft at long range, and a Thales NS100 search radar for greater redundancy and detection of low-flying incoming threats. This system also includes an electo-optical sensor to better detect threats with a low radar signature. Both of these systems significantly out-range the ship's own surface-to-air missiles, but could be used to alert other ships in the formation about enemy aircraft or redirect helicopters away from potential threats.

The electronic warfare suite aboard the ships is also new, and consists of paired large and small phased arrays which were later identified as the new "Metturi" combined ESM/ECM system. The IFF antennas, Nun-10 electro-optical scanning sensors, and Hongmoja dual-spectrum optical masts also represent elements of the Menghean Navy's next-generation sensor families.

Power and propulsion

The powerplant configuration adopted for the Hasŏ-class cruisers is similar to that adopted for the Insŏng-class destroyers. Each propeller is driven by a 55,000 kW electrical motor which connects directly to the shaft and turns at a low RPM, eliminating the need for a noisy gearbox. Electricity for the motors comes from a mix of diesel generators and gas turbine generators. Two General Electric LM2500+G4 generating 34,700 kWe each are located in a compartment in the superstructure, to maximize noise isolation and protect the main machinery compartments from flooding. Two Taesan T16J diesel generators in the hull provide low-output cruising power at 8,000 kWe each, and four Samsan 8EY26ALW diesel generators provide power for the ship's auxiliary systems. When operating in reduced-noise mode, it is possible to power the engines and all onboard systems by running a single gas turbine, though this method is less fuel-efficient as the turbine runs at reduced power.

Armament

Defensive armament consists of two 8-cell self-defense-length Mark 41 VLS modules, one on each side of the flight deck forward of the superstructure. These cells are typically loaded with a mix of quadpacked YDG-64 and YDG-67 surface-to-air missiles, for a total of 64 missiles. Both the YDG-64 and the YDG-68 have terminal active radar homing, allowing them to engage targets below the horizon with the help of an airborne radar platform. A single STIR 1.2 targeting radar above the bridge allows for direct illumination of targets in a jamming-intensive environment.

Two GBM-23/5 Bulkkot close-in weapon systems provide a second layer of protection against incoming missiles. As on the Insŏng-class destroyers, there are rumors that the Menghean Navy plans to fit directed energy weapons in place of these CIWS mounts in the future, but current reports suggest that the Unsan and Songgang will be completed with the Bulkkot CIWS.

Unlike the rebuilt Chanjok Jachido-class cruisers, the Hasŏ-class cruisers cannot carry the HŎ-3 Ryongorŭm anti-submarine missile. For long-range anti-submarine engagements, they would rely on their own aircraft, or on other ships in the formation. For emergency defense against submarines detected nearby, each Hasŏ-class cruiser is fitted with two twin 350mm torpedo tubes in fixed mounts, one on either side. In the future, these could also be used to launch anti-torpedo torpedoes, either from the existing 350mm tubes or from newly installed low-caliber tubes; as of 2020, however, no hardkill torpedo intercept system is in service with the Menghean Navy.