Sinyi-class submarine

The Sinyi class is the newest class of nuclear-powered attack submarine being built for the Menghean Navy. The class is in high-rate production at the Danyang Submarine Yard in Donggyŏng, with two boats entering service in 2018 and three in 2019. Compared with the preceding Chungsŏng-IV class, it boasts greatly improved stealth and a more sensitive sonar suite.

Development

Design work on a new nuclear attack submarine class began in 2001, after sea trials with the submarine Chungsŏng determined that the class's quieting and endurance were inadequate. Per Navy requirements, the new boat would require rafted internal hull sections, torpedo tubes on the sides of the hull, and a reactor capable of relying on natural circulation at moderate speeds. As an interim measure, mass-production of various improved Chungsŏng classes would continue until 2016.

To speed up development and control costs, a large number of components were shared between the Daedam and Sinyi classes, which were developed in parallel. The entire aft section, encompassing the reactor, turbines, aft sonars, and pumpjet propulsor, is identical between the two classes. The forward sonar and bow profile are also nearly identical, though the Sinyi class submarines incorporate an active sonar antenna in the "chin" position. The sections in between differ substantially between classes, including a completely different living area for the crew, though even here many components are shared to streamline procurement and facilitate cross-ship training.

Sinyi, the first submarine in the new class, was laid down in late 2013 and commissioned on 3 May 2018. This coincided with the planned completion of an expansion to the Danyang Submarine Yard, allowing two submarines to be laid down the following year. Since then, two new boats have been laid down every year, a high rate of production which indicates an urgent effort to close the submarine gap with the Entente Cordiale.

Design

Sensors

The Sinyi-class submarines are the first Menghean nuclear submarines to be built with all of their periscopes and electronics masts outside the pressure hull, in telescoping mounts within the 2.7-meter-tall sail. This arrangement reduces the number of openings in the pressure hull, and frees up the space normally consumed by the lower sections of the periscopes. The search and targeting periscopes are replaced by two photonics masts with visual, infrared, and low-level-light cameras, as well as laser rangefinders.

Propulsion

Like their cousins, the Sinyi-class submarines are powered by a single 200 MW RoHJ-4 pressurized water reactor. This reactor has a lifespan of 22 years between refuelings, and is crewed by seven certified reactor operators. More importantly, it is capable of relying on natural circulation to move coolant at low and medium speeds, allowing the submarine to cruise without switching on the mechanical coolant pumps. For further quieting, steam from the secondary coolant loop drives a low-speed turbine which connects directly to the propeller shaft, eliminating the need for a potentially noisy reduction gearbox. Combined with a shrouded pump-jet propulsor which prevents cavitation, these features make the Sinyi-class extremely quiet even at higher speeds.

Crew accommodations

Crew accommodations on the Sinyi class are reportedly more comfortable than accommodations on the Chungsŏng classes, but not as comfortable as accommodations on the Daedam-class, with its library, tea room, and officers' mess. All officers have personal bunks in two-person rooms, and about half of all enlisted crew must share bunks, mostly the lower ranks. There is an exercise room and a reading and electronics room, but both are relatively cramped. A spokesperson for the Menghean Navy announced in 2020 that the Sinyi-class submarines still have adequate onboard stores and facilities to support continuous 90-day missions on a single crew.

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 JWS-type submarines, the Sinyi class are designed to engage enemy nuclear submarines in the open ocean. While the Daedam-class made a number of quieting improvements, the Sinyi class take further measures, including a shorter hull which presents a smaller surface area to reflect active sonar. Their speed is also moderately higher, due to a lower displacement and reduced flow area. On a hypothetical peacetime patrol, a Sinyi-class submarine could be assigned to locate an enemy nuclear submarine and shadow it undetected, in order to promptly engage it if hostilities commence. A Sinyi-class submarine could also be sent to monitor surface and sub-surface activity in an area of interest.