A Closer Look at China’s Critical South China Sea Submarine Base

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A Closer Look at China’s Critical South China Sea Submarine Base

A deeper look at Yulin-East, China’s burgeoning submarine bastion in the South China Sea.

A Closer Look at China’s Critical South China Sea Submarine Base
Credit: Strategic Sentinel

Our previous article about Yulin-East, China’s up-and-coming submarine base in the South China Sea, provided a brief look at the base’s infrastructure and its strategic implications. Below, for those interested, we have included more information about Yulin’s features and their implications, as well as a brief technical analysis of Yulin’s strategic vulnerability.

Base Infrastructure

As could be expected, Yulin-East is positively crawling with logistical infrastructure. The geographic layout and quantity of these roadways, pipelines, radio towers, and tunnels serve as indicators of the base’s intended purpose and importance. The nearly dozen tunnel entrances to Yulin-East’s granite mountain bespeak not only redundancy, but size of the underground structure and the value of ensuring supply lines for the submarines inside. The use of a tram to schlep supplies into the mountain indicates that China plans to transport more material than a convoy of trucks could accommodate alone. The covered railway is also a safer, more resilient method of transport, but probably not resilient enough to warrant the associated costs of construction (as opposed to simply another road) unless more carrying capacity was logistically necessary. The number and size of submarine piers, the vast network of munitions transport, and the large underground facility sheltered under a mountain all indicate that China plans to accommodate as many SSBNs (and/or SSNs) at Yulin-East as possible. The Tang-class sub, the Jin’s successor, will likely need to be based at Yulin as well. The Tang-class is rumored to carry 24 JL-2 ICBMS; even if this is an overstatement, the Tang will probably be larger than its predecessor, and thus would need the wide accommodations of Yulin’s tunnel entrance.

The People’s Republic has methodically assembled the necessary force structure to make Yulin a major command and control center — and a vitally important, well-defended one in the case of a conflict. The number and size of administrative buildings suggest more officer involvement than other common Chinese naval bases. The sizeable, dense mountain makes for effective, bunkered defense in case of a major bombing raid. Yulin and Yulin-East together can house two full carrier strike groups, plus a generous handful of additional nuclear submarines. The base is designed to accommodate a wide variety of conventional and nuclear forces, some fortifying China’s strategic deterrent and others enhancing China’s coercive power in the South China Sea. Additionally, though China has been building artificial island bases at an impressive clip, the effort necessary to construct an equally-fortified base of this magnitude on a small island deep in the South China Sea would redefine herculean. (Recall that construction is still ongoing at Yulin-East after 17 full years.) Simply put, if China does want to use a base on Hainan’s southern coast as a potential command and control center for its South Sea Fleet, they have gone out of their way to make Yulin-East a qualified candidate.

The infrastructure at Yulin-East often raises more questions than answers. Do all of the tunnel entrances bored into the southeastern mountain connect to the larger internal structure? If so, identifying such entrances could provide critical information as to the size and shape of the underground facility. But some of these tunnel entrances may lead to standalone munitions or supply depots, potentially designed specifically to misdirect or confuse an adversary’s security analysts. In addition, the three radio towers could indicate an intended major Command and Control role for Yulin-East. But they could also merely serve as redundancies in case nearby radio or harbor control towers fail or are destroyed. Until we know the answers, it is difficult to determine whether some of these structures deviate from standard PLAN doctrine. We at Strategic Sentinel have flagged structures like this to watch going forward, when trends (or deviations thereof) may arise.

Striking Yulin

When discussing strike options against a military base, one must consider more than the base’s theater and point defense systems. Yulin will presumably be boasting some advanced SAM technology, if it isn’t already, and as we’ve noted, anti-ship cruise missile launchers are already deployed. But with a target like Yulin, firmly in the heart of valued Chinese territory like Hainan Island, theater and point defenses constitute merely a fraction of the threat calculus. A strike against any Hainan Island target must be considered within the context of a broader, large-scale conflict. If the United States or China wished to slap each other’s wrist, targets like Hawaii or Hainan would not be considered. Striking a highly populated, well-defended, valued piece of (undisputed) sovereign Chinese territory like Hainan Island would represent but one operation in an enormous great power war.

One of the first and most prominent challenges facing the United States in a strike on Yulin-East (read: a war with China) would be the logistical hurdle of moving forces into theater. The current US military presence in the Asia-Pacific is not enough to sustain a great power war, not even with the determined assistance of regional US allies. The necessary, massive global force restructuring alone would be challenging and expensive, rife with opportunity and financial costs not seen in decades. The United States could, certainly, successfully strike Yulin and other targets on Hainan Island. But it had better be willing to invest a vast sum of money, effort, military hardware, and lives.

Striking Yulin-East is doable, but difficult. Having already overcome the logistical and financial challenges, U.S. forces would likely need to fight their way through Chinese Integrated Air Defense Systems (IADS) in the South China Sea to reach Hainan. This could include the evasion or destruction of recently purchased S-400s that may soon guard China’s nearby artificial islands. Hainan Island is home to PLAN and PLAAF aircraft, including the J-11, which would hit the skies in a heartbeat if they detected US aircraft approaching with deadly intent. Assuming U.S. planners prioritized accordingly and deployed F-22 Raptors for the mission, these J-11s might literally not know what hit them. (The F-22 is designed to strike enemy aircraft long before they show up on their adversary’s radar.) Still, the electronic warfare environment at Hainan is increasingly dense, and the Raptor’s avionics may struggle in this theater as a result. The US could deploy the very capable EA-18 Growler electronic warfare plane to assist, but at the noticeable loss of operational stealth.

Once U.S. aircraft made it through Chinese IADS, eliminated enemy interceptors, and found a way to navigate the challenging electronic environment, the distinctions between potential theater or point defense assets at Yulin-East mean comparatively little. The United States would, as I noted before, presumably devote its most capable assets to a target as formidable as Hainan Island. The F-22 Raptors, the B-2 Spirits, perhaps some F-35 Lightnings. The detection capabilities of Chinese air defense systems do not yet pose a threat to the F-22 or B-2; whether modern air defenses can reliably identify and track the F-35 remains the subject of fierce debate among military analysts. After scaling logistical mountains and fighting their way through waves of Chinese air defenses, U.S. bombs may not even be able to penetrate the base’s mountain.

Glaring Strategic Vulnerability

China’s decision to build one submarine tunnel entrance into the mountain at Yulin-East leaves the resident submarines vulnerable to being trapped. A B-2 Spirit Bomber taking off from its base in Missouri could slide right through China’s air defense network, drop two Massive Ordnance Penetrators at the tunnel entrance, and return home. If the MOPs perform as planned, the submarine sanctuary within Yulin-East will have become a cage. Multiple tunnel entrances and exits would have mitigated this vulnerability, but it appears China made the best of what geography had to offer. The surrounding bay appears too shallow for the construction of an underwater entrance, and drilling one into the ocean-facing side of the island would be much more difficult and expensive than the current tunnel. Still, what looks like an obvious strategic flaw is likely instead a calculated risk. China’s Jin-class submarines, as second-strike guarantors, would spend as little time inside the mountain as possible. And in the case of a conflict, it would most behoove China to disperse their nuclear submarines as widely as possible, keeping them far away from obvious targets like the Yulin base.

Whether the United States’ Massive Ordnance Penetrator can even destroy the tunnel entrance is up for some debate. The MOP — a 30,000lb bomb with 5,300lbs of explosive material — is conspicuously silent about its specifications. Neither the Air Force nor Boeing has provided official statistics about exactly how far the bomb can penetrate into earth, reinforced concrete, or granite. That said, Air Force Brigadier General Hamm has explained that the MOP is specifically designed with ~20,000psi granite in mind.

Not coincidentally, high-density granite such as this protects the Iranian nuclear facility at Fordow, a major potential target of a U.S. first strike. Unsatisfied with the bomb’s progress and penetrative capabilities, the U.S. Air Force threw more money at the MOP in 2013, as tensions flamed over Iran’s nuclear program. Fordow is protected by 80 meters of granite mountain, whereas Yulin is protected by less than half that. Measured thirty meters past the tunnel entrance, the mountain’s elevation stands at just under 115ft (35m). Presumably, then, a bomb designed to hit Fordow would be capable of successfully striking the Yulin entrance. Additionally, the DOD commissioned another redesign in 2015 to further increase effectiveness. Even if the Massive Ordnance Penetrator does not successfully trap the submarines on the first pass, or if China is able to clear the tunnel entrance relatively quickly, the Pentagon could almost certainly “mow the grass” at this site as necessary.


In wartime, Yulin-East’s strategic vulnerabilities would presumably be ruthlessly exploited by the United States. No other military — not Japan’s, not India’s, not Russia’s — could reliably and successfully trap China’s submarines within their underground facility. Especially if China deploys their purchased S-400s on-site, only B-2 Spirit Bombers and F-22 Raptors could reliably turn the South Sea Fleet’s home into a cage. Though the single tunnel entrance warrants classification as an obvious design flaw, it is important to remember that it was known, accepted, and mitigated to the best of China’s ability. With only one adversary capable of leaning on the base’s most glaring vulnerability, China has deployed its best defensive equipment, built bunkers deep into the mountain, and hopes for the best.

Strategic Sentinel will be keeping a close watch on Yulin-East over the coming years as additional assets are deployed to the area. Eventually, as more nuclear submarines leave their shipyards, analysts will have a better idea of just how many submarines the underground facility can hold. We’ll be scrutinizing satellite imagery and other open sources to determine exactly which theater and point defense technologies are housed in those garages, what class of surface vessels the PLAN docks at those northern piers, and any new or ongoing construction projects. Yulin-East will be one of the most strategically valuable military bases in the Asia-Pacific, and we at Strategic Sentinel will monitor it accordingly.

Damen Cook is lead research associate at Strategic Sentinel.