Daedam-class submarine
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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 largest submarines under construction anywhere in Septentrion, and they are currently in high-rate production, with two vessels entering service 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
Characteristics
Sensors
The Daedam-class submarines carry a unique 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 flank 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.
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.
Blister-like structures on either side of the hull at the base of the sail are believed to contain non-acoustic submarine detection equipment, possibly to detect trace radioactive isotopes in the wake of a nuclear submarine.
Communications
While surfaced or at periscope depth, the Daedam-class submarines can communicate via a satellite communications mast and folding radio antenna in the sail. At shallow depths, they can also pick up high-frequency radio signals over a limited range. A towed communication buoy in the sail allows the submarine to transmit and receive radio signals while submerged.
Daedam-class submarines are also fitted with a receiving antenna for Extremely low frequency (ELF) radio signals. An ELF transmitting station in the Dzungar Semi-Autonomous Province began operation in 2017, with worldwide coverage due to the induction of the radio signal into the earth itself. Because ELF signals have a very low transmission rate (only a few characters per minute) and the submarine antenna is receive-only, this system is likely used to signal submarines to surface for further transmissions, or to send a brief coded signal indicating the outbreak of war with the Entente Cordiale.
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.
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 3.5 minutes. 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 also 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-28N has an extended range of 1,500 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 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 in 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 contains 40 torpedoes. 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 torpedo loading process is highly automated, and is rumored to be faster than the loading process on other submarine classes.
For self-defense, the Daedam-class submarines carry four YDG-61 missiles in a standard box 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.
Propulsion
The main powerplant of the Daedam-class submarines is a 200 MW 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.
If attacked, the submarine is able to deploy acoustic decoys and jammers from tubes embedded in free-flooding space in the double-hull segments.
Crew accommodations
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.