Essay: Inside the design of China’s Yuan-class submarine

(From USNI News)


China’s evolving submarine force is a topic worthy of sober examination and debate. However, for the discussion to be useful in informing both national policy-makers and citizenry alike, the content must be based on accurate data and sound analysis. Unfortunately, both are often found wanting when it comes to English-language reporting on the People’s Liberation Army Navy (PLAN). A recent USNI News essay, continues this trend. In the essay, Henry Holst, argues that the Type 039A/B Yuan-class submarine was “designed primarily as an anti-ship cruise missile (ASCM) platform capable of hiding submerged for long periods of time in difficult to access shallow littorals.”

He bases his conclusions on the Yuan’s “small” size, air-independent power (AIP) system, and long-range ASCM capability, which make it ideal to operate in shallow, coastal waters. While I wholeheartedly agree that the Type 039A/B is a fine anti-surface platform, the main points of the essay’s argument is based on a misunderstanding of largely inaccurate data. This rebuttal will examine the key points of the essay’s argument and show that the Type 039 A/B Yuan-class is, in fact, an open-ocean submarine designed to meet the needs of the PLAN’s near-seas active defense aspect of their maritime strategy, and not primarily a boat to operate in Taiwan’s coastal waters.

Yuan-Class Submarine Size

The assessment the Type 039A/B Yuan-class is a small submarine, designed to operate in the shallow littorals, is arguably the linchpin of the essay’s conclusion. A key point used in support of this position is a comparison of the Yuan-class with Japan’s Soryu-class, another AIP equipped submarine, where it is argued the Yuan is comparatively “farsmaller.”

Type 041 Yuan-class submarine

Type 041 Yuan-class submarine

In particular, Holst focuses in on the Soryu’s “draft” of 10.3 meters. This figure is highly suspect. When a submarine’s draft exceeds its beam, you might want to check your data. The 10.3-meter figure is not the draft of the Soryu class. Rather, it is the submarine’s “depth”— the vertical distance from its keel, to the top of the freeboard deck, measured at mid-length of the vessel. A submarine’s draft is included in its depth. A number of open sources list the Soryu’s draft as 8.5 meters, and a review of online photos of the fore and aft draft markings shows the draft as 8.3 meters, very close to the published value.

The description of the Type 039A/B Yuan-class submarine’s dimensions is also inaccurate. However, that reflects more the inadequacies of traditional Western sources that do not address PLAN platform and systems very well. In his essay, Holst specifically states, “PLAN naval architects deliberately maintained the Song-class’s size even with the installation of an AIP system.” While the author recognizes that trade-offs in the Type 039A/B Yuan design would have to be made, there is no attempt to suggest what they might have been. The author merely expresses his faith that the PLAN naval architects would have found a way to carve out the necessary space. This unqualified assertion is naïve at best.

Submarines are, by design, compact and severely limited in internal volume. One cannot just wave a magic wand and rearrange large propulsion plant components and squeeze out the considerable volume an AIP system requires. In particular, the cryogenic oxygen tank takes up a great deal of space—and the longer the submerged endurance, the bigger the tank. If the Song-class had that much spare volume to begin with, it would have been built smaller. There is no evidence the engineering spaces on a Song-class submarine have any extra unused volume. Video excerpts of the Type 039G show these submarines are just as cramped and constrained as one would expect. And since both the Song andYuan use double-hull construction, a designer can’t even go after the fuel load, as the vast majority of the fuel is carried in tanks external to the pressure hull. Since the Yuan has an AIP system, it has to be bigger.

A review of Google Earth and hand-held photography indicates this is indeed the case. Google Earth imagery of both submarine classes berthed near each other shows the Yuanhas a larger beam than the Song-class. This strongly argues that the sources that hold to the narrower beam of 7.5 meters for the Type 039G Song are probably closer to the truth. Furthermore, analysis of hand-held imagery indicates that the Yuan is not only longer, but also has a deeper draft than the Song-class.

Chinese submarines use the Russian system for draft markings. This means the markings do not show the draft by direct measurement, but rather it shows the deviation from an established draft. On Chinese submarines, the longer white line in the draft markings shows the submarine’s normal surface waterline, with deviations in the draft noted in 0.2-meter increments. From hand-held, broad aspect photographs of the Type 039A/B submarine, both in the water and out, one can accurately measure the waterline length and the length overall. The often-quoted length of 72 meters for the Yuan class is actually its waterline length. This value is also consistent with Google Earth measurements. The submarine’s overall length from the analysis is just over 77.2 meters, which is consistent with numerous Chinese-language websites that list the length as 77.6 meters. The same can be said of the normal surface draft that comes in at about 6.7 meters, greater than the 5.5-meter value held by many open Western source references.

Putting all of this together shows the Yuan is a large conventional submarine, only marginally smaller than a Soryu-class boat—on the order of 15 percent smaller. Perhaps a better comparison would be with the PLAN’s other large conventional submarine, the Russian-built Project 636 Kilo. That comparison shows the Yuan comes out as being slightly bigger than a late model Kilo. The table below lists the basic physical characteristics of the four submarines discussed in this article. Project 636 Kilo and Soryu-class data come from official sources, while Yuan and Song data are largely derived from the analysis mentioned above.

Thus, in stark contrast to the essay’s conclusion, the Type 039 A/B Yuan is not a small submarine at all. It is one of the largest conventional combat submarines in the PLAN inventory, and is no more maneuverable in shallow water than other large conventional submarine designs, such as the Kilo or Soryu-classes. If a navy truly wishes to invest in a “coastal submarine,” or SSC, then it would look at submarines like the German Type 205 and 206, and the North Korean Sango, all of which come in at less than 500 tons submerged displacement. Read more



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