Chuŏ-class submarine

The Chuŏ-class is the latest type of diesel-electric attack submarine developed in Menghe. The first three boats in the class were commissioned in 2020, and a minimum production run of 12 is reportedly planned, with additional orders under negotiation. The Chuŏ design makes use of an integral AIP plant to extend underwater endurance, and uses non-magnetic alloys to reduce its detectability by MAD equipment. The current, baseline model is a dedicated attack submarine specialized in hunting for other submarines, but a guided missile variant akin to the Chŏngsangŏri class is known to be in development.

Design

Layout

Like the contemporary Daedam class, the Chuŏ-class uses a mixed single-hull and double-hull design. The forward two-thirds of the pressure hull form the outer layer of the submarine, but the pressure hull narrows about halfway down the submarine's length, with an outer hull surrounding the narrower pressure hull and a compartment between the two. A free-flooding "spine" runs down the top half of the submarine, supporting the sail and other equipment.

At the aft end, the Chuŏ-class have X-shaped control surfaces, compared with cross-shaped control surfaces on most other Menghean submarine classes. This may have been done to improve shallow-water operation, or to reduce the risk of an accidental dive from a jammed aft plane. The forward diving planes are built into the hull, forward of the sail, and are short but non-retractable.

In the forward (full-width) section of the pressure hull, the top deck contains crew accommodations and the command center, the center deck contains the torpedo room and electrical equipment, and the lower deck contains the auxiliary generator, oxygen generators, and batteries. The crew accommodations are relatively generous for a diesel submarine, with most personnel assigned to personal berths rather than hot racks, though crew facilities are still less generous than those on the Daedam-class. At-sea endurance is reportedly 90 days for a standard tour, or 120 days under emergency or wartime conditions.

Armament

The main armament of the Chuŏ-class consists of eight 533mm torpedo tubes which fire directly forward. A total of 20 torpedoes are stored in the onboard magazine, and this can be increased to 28 by storing a torpedo in each tube. The center four tubes are compatible with submarine-launched variants of the YDH-26 and YDH-28 anti-ship missiles and SY-28 land-attack cruise missile; all tubes are compatible with wire-guided torpedoes.

Although all late-production Bung'ŏ-class submarines, including subclasses, had the "Long Sail" modification with a YDH-61 surface-to-air missile launcher, the first three Chuŏ-class submarines carry no such weapon system in their sails. This feature is also notably absent on the Sinyi class. Its omission has fed speculation that Menghe may be developing a surface-to-air missile which is launched through a torpedo tube in a special canister. This would eliminate a major drawback of the submarine-based YB-61/4 launcher: the requirement that the submarine partially surface to expose the sail.

Sensors

The sophisticated sonar suite of the Chuŏ-class stands as testament to their prospective role as submarine hunters. Large active and passive sonar arrays in the bow section aid in forward detection and tracking. On either side are four side-looking arrays: a large array on either side of the pressure hull, and three smaller arrays arranged along the spine structure. The large array is derived from the type used on the aft section of the Daedam and Sinyi classes, and the smaller arrays are likely used for passive ranging. The different-size arrays may be optimized for different frequencies.

Further aft, the Chuŏ-class carry a towed array sonar system which is released through a prong-like fin. This fin stands vertically upward, but is offset about two meters from the centerline. The basline Bung'ŏ-class submarines did not carry any type of towed array, a design choice which likely reflected their shallow-water mission; later models introduced a towed array system.

A final detection measure, mounted on top of the bow just forward of the diving planes, is a scanning Lidar system operating in the blue-green wavelength. Identical to the system pioneered on the Daedam class, it is able to detect a completely quiet submarine or surface ship within 100 meters or a passive blue-green emitter of the same type within 200 meters. It is tactically useless as a detection system, but when activated, it helps prevent accidental collisions between friendly submarines entering and leaving ports or operating in congested waters.

Propulsion

The Chuŏ-class is the first production-model Menghean submarine to feature an integral air-independent power unit. It uses a hydrogen-oxygen fuel cell design, based on the fuel cell module trialed on the submarne Ing'ŏ. While the basic principle is the same, however, the Chuŏ-class uses a more modern and more efficient fuel cell design. It also has an entirely different configuration: the oxygen and hydrogen tanks are stored outside the pressure hull, in a dual-hull section around the engine compartment. This ensures that if a fuel tank is damaged or develops a leak, any high-pressure flammable gas is vented outside the submarine and directly into the ocean. On the Ing'ŏ, the gas tanks are stored inside the hull itself and adjacent to the engine spaces, raising the risk of serious damage.

Apart from the AIP system, the Chuŏ-class are powered by two diesel generators. While Samsan provided the diesels on preceding Menghean submarines, these diesel generators are built by Taesan, and use a more compact design. As on the Bung'ŏ-class, total electrical output from the diesels is greater than the power rating of the electric motor, allowing the submarine to charge its batteries while running at full speed with the snorkel deployed.

Sail equipment

The sail of the Chuŏ-class is not identical to the type used on the Sinyi-class, but it is similar. The arrangement of masts is nearly identical, suggesting that design work in this area was carried over between classes. The masts themselves are fully electronic as well, and do not penetrate into the pressure hull. This allowed the designers to place the sail further forward. The masts, from fore to aft, consist of the following types:

1. Navigation radar
2. Photonics mast (search)
3. Photonics mast (targeting)
4. ESM antenna
5. FSO laser communication antenna
6. SATCOM antenna
7. Combined UHF/VHF antenna
8. Snorkel
9. Omnidirectional passive sonar receiver

Communications

In addition to the SATCOM, VHF/UHF, and FSO communication systems above, the Chuŏ-class submarines have four systems for submerged communication. First, they are capable of sending and receiving messages via underwater sound waves, though this method is used least frequently because it carries the largest detection risk. Second, they can trail an ELF receive-only antenna from the rear of the sail to detect messages sent from Menghe proper. This frequency has very low data transmission rates, and would mainly be used to call a submarine to the surface for more information, alert the submarine force to an outbreak of war, or send general status information at regular daily intervals.

The third underwater communication system is a towed communications buoy which floats just below the surface or extends an antenna above it. This, too, is a standard model used across Menghean submarine types. The fourth indirect communcation system is the Bulbit variant of the Manhwagyŏng torpedo countermeasure system, which releases a buoy that floats to the surface and broadcasts a message on repeat. This buoy can be released at any speed or depth, though it is send-only, single-use, and competes for space with torpedo countermeasure munitions. It can also broadcast a distress signal with the submarine's last location in the event of an accident.

Role

While previous Menghean diesel-electric submarines have been predominantly oriented around the anti-shipping role, the Chuŏ-class places a heavier emphasis on anti-submarine combat. It incorporates more advanced quieting measures, has a more sensitive sonar suite, and carries non-acoustic detection equipment designed to detect another submarine's wake. This suggests a possible bifurcation of roles paralleling that between the Daedam-class submarines and Sinyi-class submarines, with the Chuŏ-class hunting for enemy submarines in the Strait of Portcullia to clear the way for surface-attack submarines and surface ships.