Daedam-class submarine

3-view diagram of Daedam as built
Class overview
Builders:	Musan Nuclear Boat Facility
Operators:	Menghe
Preceded by:	Chungsŏng-III class
In commission:	2017-present
Planned:	22
Building:	8
Completed:	9
Active:	9
General characteristics
Type:	Nuclear guided missile submarine
Displacement:	Surfaced: 12,100 tons Submerged: 16,000 tons
Length:	145.7 meters
Beam:	12.5 meters
Draft:	8.5 meters (surfaced)
Propulsion:	1 RoHJ-4 PWR, 200 MWt 2 steam turbines 1 shaft 1 backup diesel generator
Speed:	Surfaced: 18 knots Submerged (silent): 20 knots Submerged: 35 knots (est.)
Range:	Refueling required after 22 years
Endurance:	150 days (maximum) 90 days (peacetime)
Test depth:	Test depth: 440 m Never-exceed depth: 570 m Crush depth: 642 m
Complement:	29 officers 103 enlisted
Armament:	8 × 533mm torpedo tube 12 × modular AShM canister (7 × YDH-28 or SY-28 each)

The Daedam class are the newest class of nuclear-powered guided missile submaries designed by Bangwigwan (formerly Institute 72) and built at the Musan Submarine Plant for the Menghean Navy. They are the second-largest submarine design under construction anywhere in Septentrion, and they are currently in high-rate production, with one to two laid down every year.

Daedam-class submarines are designed to locate and engage enemy high-value surface targets, including aircraft carriers, amphibious assault ships, and trans-oceanic supply convoys. For this role, they carry a heavy battery of 84 YDH-28 anti-ship missiles which can be launched from underwater to overwhelm large escort formations. They also have relatively generous crew accommodations, to support long-range patrols and prolonged shadowing of potential targets in peacetime.

Development

The Menghean Navy issued a design request for a dedicated guided missile submarine in 1998. The requested ship would have high endurance, good quieting, and the ability to launch anti-ship missiles underwater - in contrast to the preceding Plan 358 class, which had to surface, elevate its YDH-23 launch canisters, and then remain surfaced to provide guidance updates from a large antenna in the sail. The Bangwigwan design corporation proposed a nuclear guided missile submarine, while Ryusan, its rival, proposed a diesel-electric boat. The Ministry of National Defense approved both projects to operate in tandem, expecting that the nuclear submarine would venture out into the Meridian Ocean and the central South Menghe Sea while the diesel-electric submarine would remain in coastal waters.

One result of this divergence is that Bangwigwan's nuclear submarine would have to pass through the Strait of Portcullia at the start and end of every patrol. Innominada, on the north side of the strait, was neutral toward Menghe at the time, while Portcullia and Khalistan on the south side were both aligned with the Entente Cordiale. Running the gauntlet between them presented a serious dilemma: moving fast reduces the period of time during which the submarine is in the strait, and allows more time on station beyond it, but moving quietly reduces the probability of detection. Thus the new submarine needed the ability to run at cruising speeds while minimizing noise.

To resolve this issue, Bangwigwan's design team began development work on a new nuclear reactor designated RoJH-3. In addition to its increased power over the RoHJ-2, the new reactor would rely on natural circulation to move coolant at low to medium speeds. A prototype reactor rig was built near the Danyang Submarine Plant, consisting of a pressure hull segment floating in a pool of seawater. Here, researchers tested the reactor to ensure that it would not shut down at high banking angles, which the submarine might enter in a sharp turn. A single Chungsŏng-class submarine, designated Chungsŏng-IA in the West, was completed with a RoJH-3 reactor for testing, and is easily identifiable by a "hunchback" distortion just aft of the sail. Work on the reactor proved to be one of the main bottlenecks in developing the new submarine; initially the Navy was satisfied with a natural circulation speed of 10 knots, but after relations with Innominada broke down in 2005, the Navy upped the low-noise speed requirement to 20 knots.

The relentless drive for quieting drove a number of other design choices. Instead of a conventional propeller, the new submarine would use a pump-jet propulsor, greatly reducing the noise from cavitation. It is also the first Menghean submarine class to use fully rafted interior construction, insulating noise from non-engine systems. To reduce flow noise and drag, the hull was built to a perfectly circular cross section with as few openings as possible.

Early on in the development process, it became clear that the new submarine would be too long to fit in the construction hall at the Danyang Submarine Plant. To address this issue, and to increase building capacity, the Ministry of National Defense financed the construction of a new submarine building hall in the city of Musan. Upon completion, it became the largest structure of its kind in Menghe; by one expert's assessment, it is capable of holding ten or more Daedam-sized submarines in various stages of construction.

Characteristics

Sensors

The Daedam-class submarines carry a new type of spherical sonar array in the nose. Little is publicly known about this system, but it reportedly offers greatly improved sensitivity compared to preceding Menghean submarine sonars. Large side-looking sonar arrays on either side of the hull complement this system; they are placed on double-hull sections of the hull, allowing the sonar equipment to be recessed into the free-flooding internal space. In addition to the large flank arrays around the missile tube section, there are medium-size arrays on either side of the engine compartment, and smaller arrays on either side of the sail. The reason for the different sonar arrays is unknown, but they may be optimized for listening in different frequencies. There are small sonar antennas on the fore and aft ends of the sail.

Further aft, the submarines have two deployment points for towed sonar arrays, one at the end of each horizontal stabilizer. This suggests the use of either two towed array sonars in different frequencies, or one towed array sonar and one towed torpedo countermeasure system. The spools for both towed arrays are located inside the aft free-flooding space.

On top of their sonar arrays, the Daedam-class submarines carry a sophisticated non-acoustic detection system which was tested on late-model Chungsŏng-class submarines. The visible elements of this system consist of a blister-like structure on top of the nose; a tower or periscope like structure on top of the sail; and small groups of probes on either side of the sail. While the exact workings of the non-acoustic detection system are classified, it likely works by detecting trace chemicals and temperature differences which are left in the wake of a nuclear submarine.

Also atop the bow is a rotating conical antenna with laser emitters and receivers. This is a special Lidar-based collision avoidance system using blue-green lasers. Menghean sources claim that it has a range of 100 meters, and is invisible to passive detection within 200 meters; blue-green light penetrates seawater better than other frequencies, but is still absorbed very quickly in absolute terms. This system is intended as a final line of defense to prevent collisions between ultra-quiet submarines, which have taken place on multiple occasions in other navies.

Sail

The Daedam-class submarines have an unusually long and low sail. They also use masts and periscopes which penetrate through the pressure hull, unlike the contemporary Sinyi-class submarines, which have fully enclosed masts outside the pressure hull with electronic feed to screens inside the control room. Designers reportedly chose the low sail structure in order to improve navigability in shallow waters, and in a belief that it would reduce flow resistance.

From fore to aft, the sail houses the following retractable masts:

1. Targeting periscope
2. Navigation radar
3. ESM dome
4. Air search radar
5. Search periscope
6. FSO communications antenna
7. SATCOM antenna
8. ESM and HF/DF antenna
9. UHF and VHF radio antennas
10. YB-61/4 retractable missile launcher
11. Snorkel (for backup diesel engine)
12. Retractable ELF receiver antenna

The periscopes are partial photonics masts, in that each is topped with an electro-optical unit containing a visual-spectrum camera, a low-light camera, an infrared imaging camera, and a laser rangefinder. These feed imagery to high-resolution LED screens inside the hull, and can automatically track a target and estimate its speed and bearing. As with a conventional periscope, however, the lower half of the mast retracts into the hull through a gap in the pressure hull.

Communications

In total, each Daedam-class submarine is known to use the following communication methods, ranked in order of decreasing safety. Systems from 5 onward require the submarine to raise a retractable mast above the surface of the water, which can reveal its location.

1. ELF receiver antenna, towed from the sail
2. Towed variable-depth buoy with retractable radio antenna
3. Bulbit single-use signal buoy
4. Acoustic communication antenna
5. Satellite communication antenna on retractable mast
6. FSO communication block on retractable mast
7. Combined VHF and UHF antenna on retractable mast

The towed buoy system uses a remotely controlled vehicle held to the submarine by a transmitter cable. It ascends to just below the surface, where Very Low Frequency radio waves can penetrate into the water, for a receive-only mode. It can also extend its own antenna mast above the surface, allowing two-way transmission in the HF, VHF, and UHF frequency bands, at the cost of exposing the submarine to active and passive radar. Two towed buoys are carried under square hatches just above the engine room; they appear to be about 3-4 meters long and 500 millimeters in diameter, with an irregular front shape. Given their size, it is possible that these buoys can also function as a buoyant variable-depth sonar, passively listening to acoustic emissions above the thermocline while the submarine patrols at a lower depth. If so, its range is likely limited by the small antenna.

VLF and ELF are the only frequencies which can penetrate far enough below the surface of the ocean to reach the submarine at all times, i.e. when it is not deploying a mast or buoy. A drawback of these frequencies is that they require enormous transmission antennas, on the order of several kilometers, to send messages. Menghe began operation of one such ELF facility in 2017, but the submarine systems are still receive-only. VLF and ELF also have extremely low data transmission rates, equivalent to a few characters per minute. It is believed that the Menghean Navy uses its VLF and ELF systems for two functions: first, as a "bell" to call individual submarines to the surface for further communication; and second, as a "drum" alerting all submarines on patrol that Menghe is in a state of war with a given country. Daily communications also update patrolling submarines on the alert state and other key information.

The Bulbit single-use signal buoy is a variant of the Manhwagyŏng torpedo countermeasure which floats to the surface and broadcasts a pre-recorded message on pre-set frequencies for a pre-programmed period of time. Because it cannot be recovered once launched, and because each stowed Bulbit takes away space from another decoy or jammer, the Bulbit system is mainly used when there is no time to deploy the towed buoy or when the submarine is moving at a high speed. If the submarine sinks or is damaged, the crew can launch a Bulbit buoy which broadcasts intermittently for 48 hours with a distress signal containing the coordinates of the accident, alerting rescue crews to the submarine's status.

In addition to radio-frequency communication methods, the Daedam-class submarines have an underwater acoustic communication system capable of broadcasting and receiving messages via pulsed sound waves in water. This allows for communication with surface ships, submarines, and seabed transmission antennas. Because it requires active transmission, however, it can give away the submarine's location on passive sonar.

In 2019 a research team affiliated with Haeju Engineering-Technical University announced that they had successfully transmitted an instantaneous signal between two quantum-entangled photons, one of them in an underground compartment. The Menghean Ministry of National Defense is rumored to be studying the applications of quantum entanglement to submarine communication.

The Menghean Navy is known to have looked into blue-green lasers for aircraft-to-submarine communication, though this research has struggled with the question of how to reliably pinpoint the submarine's exact location. The Daedam-class submarines do feature a Free-space optical communication mast on the sail, which is designed for use on the surface but may have sub-surface capability.

Armament

The main armament of the Daedam-class submarines consists of twelve large vertical launch cylinders in the middle section of the hull. In the boats' current configuration, each of these contains seven launch tubes for the YDH-28 anti-ship missile, for a total of 84 missiles carried. These missiles can be launched from a depth of 150 meters, and can launch at 2-second intervals, allowing one submarine to launch all 84 missiles in 3 minutes and 30 seconds. Before launch, the missiles can be individually programmed to follow angled courses toward the target, in order to overwhelm it with attacks from multiple directions, deliver all missiles to the target simultaneously, and avoid revealing the location of the launch platform. In flight, the missiles communicate with one another via datalink in order to allocate targets efficiently and detect a moving fleet more easily.

The individual launch tubes can also fire the SY-28, a land-attack cruise missile based on the YDH-28. The SY-28JG has an extended range of 1,000 kilometers, and missiles launched later in the strike can perform a post-strike damage assessment by transmitting data from the onboard targeting camera.

The seven-tube launch apparatus for the YDH-28 is designed to be removed and replaced as a single unit for rapid re-arming and maintenance in port. This approach also allows the submarine to be fitted with different vertical launch modules. Possible future options include high-endurance UAVs for reconnaissance and damage assessment; supersonic and hypersonic anti-ship missiles; and a submarine-launched anti-ship ballistic missile with a maneuvering hypersonic re-entry vehicle, rumored to be in testing as of 2020.

In addition to their missiles, each submarine is fitted with eight 533mm forward-facing torpedo tubes. Unlike the torpedo tubes on the Chungsŏng-class submarines, these torpedo tubes are arranged along each side of the hull, and point outward at an angle of 10 degrees. This keeps the turbulence from the torpedo firing hatches further from the sonar, reducing "self-deafening" at high speeds.

The internal magazine stretches over two decks and features a moderately high level of automation. In addition to wake-following and sonar-homing torpedoes, the Daedam-class can launch torpedo-tube-fired anti-ship missiles, though these are rarely loaded because of the existing vertically launched missile armament. The internal magazine itself carries 40 torpedoes, or five per tube, but this total can be increased to 48 by storing ready torpedoes in each of the eight tubes.

For self-defense, the Daedam-class submarines carry four YDG-61 missiles in a YB-61/4 launcher on a custom swiveling arm. This weapon can engage helicopters and low-flying patrol aircraft. When the submarine is submerged, the launcher retracts into a watertight cylinder in the rear of the sail; it can only extend while the submarine is fully surfaced. Both the electro-optical search periscope and the retractable short-range radar mast can acquire and range targets, and because the missile uses infrared homing guidance it does not require an onboard target illumination antenna.

Propulsion

The main powerplant of the Daedam-class submarines is a 200 MWt RoHJ-4 pressurized water reactor. This new-generation reactor design is arranged with the primary cycle heat exchange raised above the reactor to allow convection-type flow. At higher output levels, pumps in the reactor compartment circulate coolant. Steam from the secondary loop powers a large direct-drive steam turbine, which drives the shaft to a shrouded pump-jet propulsor. Independent estimates suggest that the submarine can achieve a maximum speed of 35 knots when submerged.

In addition to the nuclear reactor, there is also a diesel generator in the lowest level of the crew section. This is normally turned off, leaving the quieter reactor to generate all electricity. The generator exists mainly as a backup system, to run the reactor control systems in an emergency or bring the submarine to port at low speed if the reactor is damaged.

The RoHJ-4 reactor contains enough high-enriched fuel to run for 22 years without replenishment. Work is reportedly underway on a next-generation reactor with a 32-year lifespan, which would eliminate the need for a mid-life refueling and overhaul altogether.

Quieting and countermeasures

The Daedam-class submarine was designed to achieve a high level of quieting in order to evade detection when approaching targets with surface escorts. They are the first Menghean nuclear submarine class to be built with all interior compartments assembled from raft modules, rather than rafting the machinery alone. Many components are double-rafted, with noise-absorbing rubber mounts linking the machine to the floor and the floor to the pressure hull.

The powerplant is designed for especially quiet operation. The RoHJ-4 reactor relies on natural circulation to move the primary coolant at low and medium power output levels, and Menghean sources claim that the submarine can travel at speeds of up to 20 knots without activating the primary coolant pumps. Even when the primary coolant pumps are running, efficient pipe arrangement and double rafting reduce the resulting noise.

The reduction gears linking the turbine to the propeller shaft - a major source of noise on the Chungsŏng-class - were eliminated altogether by having the main steam turbine run at a reduced speed. This required a much larger turbine in order to maintain efficiency. The use of a pump-jet propulsor greatly reduces the level of cavitation by shrouding the tips of the propeller blades.

The submarine carries a total of 48 launch tubes for Manhwagyŏng torpedo countermeasures, the maximum number permitted on a single Manhwagyŏng suite. These are loaded in twelve four-tube batteries arranged between the pressure hull and the outer hull of double-hull sections forward and aft of the reactor compartment, and can be ejected at any depth or speed at which the Daedam class operates. The mounts do not create openings in the pressure hull itself, and can all be reloaded from above the waterline while the submarine is docked.

Crew accommodations

Multi-view cross section of a Daedam-class submarine. Note the generous dining and activity areas on the mess deck.

In contrast to the Chungsŏng class boats, which were reportedly cramped and uncomfortable, the Daedam-class submarines have relatively generous crew accommodations. A Menghean state news report touring the lead boat showed a large mess hall, an exercise room, a briefing room, and a well-decorated lounge which includes a library with books and electronics. Menghean news reports have also referred to a "tea room" aboard the submarines, though this apparently refers to the officers' lounge rather than a dedicated tea space. Footage from the tour also showed wood paneling, or paneling in a fireproof wood substitute, in many crew areas.

Foreign intelligence agencies have also noted that the crew count for the Daedam-class submarines is relatively large compared to previous Menghean and similar Letnian submarine classes. While some of this increase stems from the submarine's large size, it is also consistent with an effort to reduce each crew member's workload and conduct more maintenance at sea. Combined with the improved accommodations, these changes suggest that the Daedam-class submarines are intended to conduct longer patrols further from friendly ports and bases.

Role

In the Menghean Navy's ship classification scheme, the Daedam-class submarines are categorized as Nuclear Attack Submarines (공격 원자력 잠수함 / 攻擊原子力潛水艦, Gonggyŏk Wŏnjaryŏk Jamsuham), and the Sinyi-class submarines are categorized as Nuclear Patrol Submarines (순찰 원자력 잠수함 / 巡察原子力潛水艦, Sunchal Wŏnjaryŏk Jamsuham). While most other navies group these together as attack submarines, the Menghean Navy considers them separate types, following a bifurcation of the nuclear submarine force in the 2000s. In this division of roles, JWS hulls specialize in tracking, shadowing, and engaging enemy submarines, while JWG hulls specialize in engaging surface ships. Each type has the ability to cover the other's duties if required, but their designs reflect different priorities and their mission orders are built around their respective advantages.

As Menghe's first dedicated Nuclear Attack Submarines, the Daedam class are designed to patrol blue-water areas and intercept hostile high-value surface targets approaching the Hemithean theatre. Such targets could include troop transports, amphibious warfare ships, supply convoys, and, in a prolonged war, civilian shipping. The most important targets, and the most challenging to engage, would be aircraft carriers and their escorts. With 84 ready-to-launch YDH-28 missiles, programmed to approach the target from a variety of directions and arrive in the same window of time, a Daedam-class submarine has the potential to single-handedly neutralize a carrier battle group by overwhelming it with more threats than its missile defense can handle. Large missile and torpedo magazines also give each submarine a large number of "stowed kills," allowing it to remain on station for a long period and complete multiple small anti-shipping missions before returning to base to re-arm.

Beyond the anti-shipping role, the Daedam class can also carry out other missions when equipped for them at a base facility. The seven-cylinder vertical launch modules are fully compatible with the SY-28 missile, a land-attack derivative of the YDH-28, which can strike stationary targets from a range of 1000 kilometers. The 533mm launch tubes are also believed to be compatible with torpedo-tube-deployed undersea mine systems; other sources suggest that a dedicated minelaying module can be installed in place of the seven-cylinder missile module. Minelaying, however, is most likely left to Menghean diesel-electric submarine classes, which are better oriented toward operations in coastal areas.

Construction

All Daedam-class submarines are built at the Musan Nuclear Boat Facility in Musan, southeastern Menghe. This shipyard was specifically constructed for the Daedam-class, as the new submarines were too long for the main assembly hall at Danyang. It consists of a massive hangar structure capable of assembling four Daedam-class submarines and fitting out several more. This is one of the largest enclosed structures of its kind in Septentrion. Because of the submarine's rafted construction, pressure hull segments are linked first, and interior rafted sections built in an adjacent warehouse are then loaded into them.

The first submarine in the class, JWG Daedam, took nearly eight years to complete, the longest construction period of any Menghean submarine. Most of the delays related to the new reactor plant, which had to undergo additional testing and development work in order to increase its natural circulation speed. Fitting-out also took four years, as shipyard staff corrected design errors and resolved unexpected problems during sea trials. Apart from these problems, the Daedam-class are also the largest Menghean submarine class ever built, which in itself became a source of delays.

Over time, however, the Musan Nuclear Boat Facility was able to resolve these problems on future hulls while streamlining the building process. Construction times for subsequent hulls steadily dropped, with Sinjung completed in a record 4 years, 11 months, and 22 days.

The rate of construction of Daedam-class submarines surprised many foreign analysts, who had expected a modest production run similar to the later Chungsŏng types. Instead, Menghe has laid down new Daedam-class submarines at a rate of two per year since 2013; in March 2018, there were no fewer than 12 Daedam-class submarines at various stages of construction. This ambitious building program suggests that the Menghean Navy is placing a greater emphasis on nuclear submarines as the mainstay of its anti-carrier operations.

Deployment to Kolodoria

Possible route of a Daedam-class submarine from the base site in Kolodoria to a launch position off the coast of Casaterra. The blue-shaded circle shows the approximate strike radius of an SY-28 cruise missile in its basic (non-extended-range) variant.

In 2019, it was revealed that Menghe had been in negotiations with Kolodoria over the building of a nuclear submarine base on the latter country's west coast. A site on the north coast of the Jedorian Sea was selected in 2020. Independent estimates suggest that the facility will be able to support up to four nuclear submarines when completed, and they will likely be Daedam-class vessels. Submarines at this base will be able to freely enter the Crimson Sea without passing through the Maw.

Ostensibly, the purpose of this base is to allow Menghean submarines to intercept EC warships, including carrier battle groups, heading westward to the Maw. If armed with SY-28 cruise missiles, however, they would also be able to attack land targets in any part of Anglia and Lechernt, Sylva, or, with the extended-range variant, Sieuxerr. Combined with a worldwide-coverage ELF broadcasting system for war-outbreak alerts, this would allow Menghe to launch precision attacks on Entente governnment buildings or uranium enrichment facilities in the event of an outbreak of war. Previously, Menghe possessed no capability to strike targets on the continent of Casaterra, and claimed to have no intention of doing so.

The Kolodorian submarine base has become a major source of controversy in the region, as it has the potential to seriously tip the balance between Menghe and the Entente. Fyrish diplomats have cited the base as evidence that Menghe aspires to build worldwide force projection capabilities. As of August 2020, construction on the base is still underway, and analysts consider it likely that Menghe will deploy two new-build Daedam-class submarines there before the end of 2021.

Saryŏ subclass

In March of 2021, rumors emerged that the 14th boat in the class, Saryŏ, was being built to a special "stretched" configuration. According to these reports, which are still unconfirmed, Saryŏ will be completed with a deep-sea special forces module in place of the missile module, and will feature an airlock or a docking point for a deep-sea submarine. Thus far, state sources have vigorously denied these rumors, and the Musan construction facility is fully enclosed and off-limits to visitors, making it impossible to confirm these reports. An annual military shipbuilding report released by the Military Publicity Agency in 2020 listed Saryŏ under the hull number JWY-983, with JWY denoting a nuclear-powered missile submarine rather than a special type. This may, however, be an effort to mask the submarine's true purpose.

Boats in the class

Name	Meaning	Builder	Laid down	Launched	Commissioned	Status
Daedam	Courage	Musan	2009 Sep 30	2013 Jul 13	2017 Jun 14	In service
Gyŏlsin	Determination	Musan	2010 Mar 01	2014 Jan 15	2018 May 07	In service
Yonggam	Bravery	Musan	2011 Jul 07	2014 Sep 02	2018 Sep 10	In service
Chungjik	Loyalty	Musan	2012 Aug 07	2015 Apr 26	2019 Jan 12	In service
Yongmeng	Courage	Musan	2013 Jul 20	2015 Jun 12	2019 Aug 28	In service
Munmyŏng	Civilization	Musan	2014 Jan 19	2016 Sep 15	2019 Oct 27	In service
Damyong	Daring	Musan	2014 Aug 08	2017 Feb 15	2020 Jan 16	In service
Sinjung	Caution	Musan	2015 Apr 30	2017 Dec 03	2020 Apr 21	In service
Chongmyŏng	Sagacity	Musan	2015 Jun 16	2018 Feb 11	2020 Dec 22	In service
Gyohwal	Cunning	Musan	2016 Sep 21	2018 Dec 17	2021	Fitting out
Mussang	Unmatched	Musan	2017 Feb 22	2019 May 07	2021	Fitting out
Hyŏnmyŏng	Wisdom	Musan	2017 Dec 11	2020 Apr 23	2022	Fitting out
Hoham	Dauntless	Musan	2018 Feb 17	2020 Aug 21	2022	Fitting out
Unnamed hull	N/A	Musan	2019 Jan 01	2021	2023	Building
Unnamed hull	N/A	Musan	2019 May 13	2022	2024	Building
Unnamed hull	N/A	Musan	2020 Apr 27	2022	2025	Building
Unnamed hull	N/A	Musan	2020 Aug 26	2023	2025	Building

See also

• Chungsŏng-class submarine
• Sinyi-class submarine
• Chuŏ-class submarine