Chungsŏng-class submarine

The Chungsŏng class is a class of nuclear-powered attack submarine designed and built in Menghe during the 1990s and 2000s. There are three major subclasses, known in the West as Chungsŏng-I, Chungsŏng-II, and Chungsŏng-III. With a teardrop hull, a streamlined sail, and a variable-depth sonar pod, they represented a major development leap over the preceding JW-351 class. Menghean news sources also claimed that the Chungsŏng-class had achieved a very high level of acoustic quieting, on par with contemporary nuclear submarines. In reality, while stealthier than the noisy JW-351s, the Chungsŏng-class submarines were still judged insufficient by the Navy, which ordered the development of a more advanced replacement class.

Development

Menghe's first nuclear-powered submarine, JW-351, was laid down in 1978 and commissioned in 1983. Though she carried torpedo armament and combat sensors, the Menghean People's Navy ultimately regarded the JW-351 design as an experimental prototype rather than a production-ready submarine. Before JW-351 even began her sea trials, Institute 72 - tasked with the design of nuclear submarines - began development of a more modern successor class. This project proceeded slowly, however, and as an interim measure the DPRM laid down the JW-352 and JW-353, both of them modified derivatives of JW-351.

After the Decembrist Revolution, the Interim Council for National Restoration decided to cancel the construction of a fourth JW-351 hull, but finish fitting-out of the JW-353. Development of the successor class briefly stalled as well, but in 1990 Institute 72 was ordered to resume design work. The first hull segment of the new submarine class was laid down in secret on December 18th, 1994.

The design of the new submarine class reflected shifting priorities in the Menghean Navy, as Rear Admiral Sun Yŏng-gi took over the post of Vice-Marshal of the Submarine Force. While JW-351 followed a double-hull design, the new submarine used a single-hull layout, which Sun believed would be cheaper to mass-produce. While JW-351 had a reserve buoyancy factor of 38% and extensive internal watertight barriers, allowing her to surface even if one segment and the surrounding ballast tanks were ruptured, the new design had a reserve buoyancy factor of only 12% and had only rudimentary watertight segmentation. This approach reflected Sun's conclusion, on reviewing past domestic and foreign submarine accidents, that even if a damaged submarine were to surface it would either succumb to flooding while adrift or sink from an enemy follow-up strike.

In 1996, it was reported that Menghe had obtained a computer-controlled propeller milling machine from a Hallian shipbuilding company after ordering it through a state-owned civilian shipbuilder. This machine was likely used in manufacturing the low-cavitation propellers for contemporary submarine classes.

The Ministry of National Defense initially anticipated a production rate of 1 hull per year by the end of the decade. The actual construction process, however, soon encountered delays and cost overruns. Plans to have the first submarine in service in time for the 10th anniversary of the Decembrist Revolution were postponed, and an audit in 1998 found the project to be more than 50% over budget. Faced with a budget that was barely keeping pace with inflation, the Navy scaled back its procurement plan, aiming to have four submarines in service by 2005.

The first ship in the class was commissioned on October 9th, 1999, under the name Chungsŏng ("Loyalty"). This made her the first Menghean military submarine in pre- or post-war history to receive a name, rather than a mere hull number. As the Disciplined Society Campaign was still in full swing, the Ministry of National Defense decided to name all four ships after virtues, and future Menghean nuclear submarines carried forward this tradition. Choe Sŭng-min himself reportedly took part in the ship naming process, selecting Chungsŏng from a list of options as the name of the first hull.

Leaked photographs of the Chungsŏng caused considerable surprise in the West, as the submarine's external appearance suggested a major leap in design compared to the JW-351. Menghean news sources fueled additional speculation, claiming that the new submarine was on par with the latest Glasic and Dayashinese designs in terms of stealth and performance.

Speaking to a group of Dayashinese military officers in 2016, Rear Admiral Sun Yŏng-gi claimed that on several occasions Menghe had held simulated acoustic testing exercises in the East Menghe Sea while secretly keeping Chungsŏng in the Kimhae Sea, in order to give the impression that the submarine was present but undetectable to Dayashinese surveillance ships.

Even after her commissioning, Chungsŏng spent the first few years of her service life conducting sea trials. At first trials were held in the East Menghe Sea, but before the end of 1999 they moved to the South Menghe Sea out of fears that Dayashinese intelligence assets would be able to monitor the tests. In addition to familiarizing the crew with the design, these trials aimed to assess the ship's noise levels, identify design defects, and gain experience in developing nuclear submarine doctrine. In classified documents that were released in the late 2010s, officers assigned to the trials related serious issues with the Chungsŏng design, including noise levels well above the expected levels. The cruiser Chanjok Jachido, fitted with an advanced Hallian AN/SQR-19 towed sonar array, proved especially adept at finding the submarine in exercises.

Characteristics (Chungsŏng-I)

"Chungsŏng-I" is the Western designation for the first batch of four submarines in the class. As with surface ships, the Menghean Navy names each subclass after the first ship completed to the modified design, but some of these ship names were not known internationally when first photographed.

All Chungsŏng-class vessels use a streamlined teardrop hull with a blended sail, making them similar in appearance to Letnian submarines such as the Akula class. Unlike Letnian submarines, however, the Chungsŏngs use a single-hull design, in which the reinforced pressure hull is also the outermost layer. Only the forward and aft sections are free-flooding with ballast tanks.

In the bow, the submarine carries a cylindrical sonar array in the "chin" position, with a distinct sonar-transparent window around it. Above this are eight 533mm torpedo tubes arranged in two rows of four. Early intelligence reports erroneously described the armament as four 533mm and four 650mm torpedo tubes. Post-commissioning trials found that at high speeds, water flow over the doors of the torpedo tubes generates excessive noise in the forward free-flooding compartment, interfering in the ship's sonar and leaving the submarine blind. Total magazine capacity is 40 torpedoes.

Survivability in the event of an accident is relatively poor. While there are five watertight bulkheads in the internal hull, these are only reinforced to contain low-pressure water near the surface, and will rupture if the boat floods near its maximum depth. Reserve buoyancy is also relatively poor; the submarine is not designed to continue fighting or attempt a return to port if its hull is breached. Instead, standard operating procedure is to shelter the crew in two rescue chambers - one at either end of the hull - and decouple these from their recesses, bringing the survivors to the surface. The loss of the diesl-electric submarine J-655 to an at-sea accident in 1995 led to a re-examination of this approach, but by that time it was too late to modify the design under construction.