Yechŏn-class frigate

The Yechŏn-class frigates are a class of warship built in Menghe during the 2000s and early 2010s. The type has also been exported to a number of other countries, including Idacua and Azbekistan. Produced in large numbers, it comes in a variety of subtypes and refits, both in Menghean service and when sold abroad. It was succeeded by the Chunchŏn-class frigate, but remains in service and is still considered highly capable in the fleet escort role.

Role

The Menghean hull type of the Yechŏn-class is HO, for Oechŭng Howiham (외층 호위함 / 外層護衞艦), or "outer-layer escort ship." This hull classification was first applied to the Ansa-class frigates, to distinguish them from the larger Pyŏng'an-class destroyers. The Yechŏns, however, were the first Menghean frigates to fully exemplify the HO type.

As the name implies, outer-layer escort ships are designed as defensive escorts for a carrier battle group, amphibious battle group, or convoy, and would either form an outer defensive ring around the protected unit, or position themsvelves on the threat axis between the protected unit and a suspected enemy. They are primarily designed around the anti-submarine role: "main force escort ships" (Juryŏk Howiham) provide the long-range anti-air umbrella for the escorted formation, and engage any submarines which pass through the outer escort ring.

Because they can rely on other ships for long-range air defense, outer-layer escort ships in Menghean doctrine are not armed with long-range air defense suites. Their outer position, however, puts them between the main fleet and any enemy threat, and makes them vulnerable to being picked off ahead of a larger strike. For this reason, ships in this design require a highly capable short-range air defense system, even as they lack long-range air defense capabilities. This requires a fast-scanning radar high on a mast (to extend the distance to the radar horizon and a short-range surface-to-air missile armament which can engage many low-level targets in rapid succession. This distinguishes outer-layer escort ships from medium anti-submarine patrol ships, like the Ginam and Mirun classes, which have minimal anti-air armament as they are designed to patrol areas with a reduced enemy air and surface threat.

The final constraint on the type is cost. Because of its intended role of escorting a high-value target at the outer ring of a formation, the Yechŏn class and its successors are likely to suffer high attrition in the event of a war. To increase the number of outer escorts, and reduce the blow inflicted by each loss, designers were pressured to leave out any capabilities not directly relevant to the above mission. Thus, the class's capabilities for coastal bombardment, special forces insertion, mine clearance operations, and littoral combat are very limited, and in the class's initial iteration, so were its anti-ship capabilities.

Development

Preliminary design work on a new frigate class began in the mid-1990s, while work on the Ansa-class frigates was still underway. The Navy solicited a range of designs, under the common heading of "New Century Warship" (Sinsedae Jŏnham), but tight defense budgets during the late 1990s and early 2000s meant that no definitive orders would be placed until 2002. Many of the more ambitious designs, including one Plan 83, incorporated the Glasic Mark 41 Vertical Launching System and LM2500 gas turbine, but Tír Glas remained noncommital about whether to sell or license these systems due to objections from Dayashina. Menghean naval procurement staff viewed the former system as particularly important because the Ansa and Hawŏn classes had YDG-37 (licensed Uragan missile systems, but with single-arm launchers and SARH guidance that greatly limited their effective target engagement rate. The noisy HŎ-2 Poksŏl anti-submarine weapon was also in need of replacement.

A breakthrough came in 2001, when Choe Sŭng-min agreed to resolve the Renkaku Islands dispute with Dayashina as part of a debt forgiveness deal following the 1999 Menghean financial crisis. This settled a lingering source of tensions between the two countries, and led the Dayashinese government to green-light arms sales of less-sensitive equipment to Menghe. With that technical hurdle cleared, the Menghean Ministry of National Defense authorized the construction of six frigates of the Plan 83 type. The contract specified that three would be built by the Gyŏngsan Songsu-do Shipyard and three by the Kimhae Naval Yard in Donggyŏng, to keep both facilities in operation during a period of modest spending.

Yajjdan subclass

Upon reviewing lessons from the Battle of the Aqaba Sea, Menghean Navy doctrinal planners concluded that inadequate short-range missile defenses were responsible for the loss of the destroyer Bŏmram and the frigate Bupyŏng in air-launched missile strikes. To address this issue, they ordered that subsequent Yechŏn-class frigates be completed with a 24-missile YDG-61 launcher on top of the helicopter hangar, facing aft. This, in turn, required strengthening the hangar structure and raising the aft missile illumination radar, meaning that the changes could not be applied to ships already under fitting-out. The first ship built to the new standards would be Yajjdan (sometimes transliterated Yazdan), laid down in late April 2006.

Yajjdan and the three ships that followed her (Hongsa, Pyŏngsŭb, and Buyŏ) are sometimes considered a separate subclass, due to their enhanced missile armament, reinforced hangar, and modified profile. Interestingly, however, the Menghean Navy did not issue a separate class name for this group, as it had done with the Hyŏngnam-class destroyers (a Yobu subclass) and Hawŏn-class frigates (an Ansa subclass), or for that matter the Dŏkju subclass which followed. Instead, Menghean sources sometimes refer to them as a "modified Yechŏn group" or "Yechŏn variant."

The initial report leading to the Yajjdan subclass suggested that similar refits be made to existing ships, though this likely would have required a lighter YDG-61 launcher or serious rebuilding, if it were practical at all. In 2008, however, the development of the YDG-7N missile meant that the forward Mark 41 self-defense cells could be loaded with quad-packed surface-to-air missile canisters, increasing the maximum SAM loadout of the forward cells from 16 missiles to 64. This was, in practice, excessive, and most actual loadouts carried 36 or 48 missiles forward. Such a change was judged adequate to eliminate the need for a secondary YDG-61 launcher, even as Yajjdan was still in fitting-out.