There has been extensive debate in recent years about modern Chinese anti-access/area-denial (A2/AD) systems rendering the aircraft carriers of the United States Navy (USN) highly vulnerable if Beijing and Washington were to clash in the western Pacific. Particularly ominous is the growing undersea arm of the People’s Liberation Army Navy (PLAN). According to the U.S. Office of Naval Intelligence, China’s attack submarine fleet consists mainly of diesel-electric boats (SSKs) – there are 57 of them, as well as five nuclear-powered attack submarines (SSNs). Of these, the more modern ones include two Shang SSNs, 12 Kilo SSKs, and 12 Yuan SSKs.
Experts often allude to the threat posed by SSKs to the U.S. flattop. This is because the SSK, which is quieter than its nuclear-powered counterpart, is seemingly often able to slip detection by the carrier’s escorts. There have been numerous instances of American carrier groups being surprised by SSKs, friendly or otherwise, during either training exercises or regular deployments. The most famous is arguably the 2006 incident of a Song surfacing at a distance within firing range of the Kitty Hawk battle group. Critics point out that if a relatively inferior sub like the Song was able to penetrate the carrier’s screen, a more capable one such as the Kilo would find the endeavor easier. And in a similar case in October this year, a Chinese boat reportedly “stalked” the Reagan carrier strike group (CSG), setting off alarm bells amongst U.S. defense officials. So the question is to what extent would PLAN submarines threaten U.S. carriers during a conflict? This questions has two parts: 1) assessing how likely it is that a Chinese boat would be able to locate and track the American capital ship, and, 2) if it is able to do so, the extent to which it damage or sink the flattop.
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Chinese submarines are likely to be forward deployed in a cordon to intercept the American CSG as it transits to the conflict zone in the western Pacific, with SSKs acting essentially as mobile minefields owing to their limited speed and endurance. Regarding the issue of Chinese subs finding U.S. carriers, Peter Howarth asserts in his book China’s Rising Sea Power: The PLA Navy’s Submarine Challenge (Routledge, 2006, p. 103.) that in the event of a Taiwan contingency:
The PLA Navy’s most promising course would be to deploy its quiet… SSKs to stake out the chokepoints between the chain of islands along the East Asian continental shelf and lie in wait for carrier… groups as they make their way into the semi-enclosed areas off the China coast.
China’s considerable progress in the A2/AD realm during the years since that study was published means that U.S. CSGs would be reluctant to operate in the “semi-enclosed areas off the China coast,” which is the area within or around the First Island Chain. As such, they are likely to operate beyond that – in the Philippine Sea and beyond. (See map below.)
Source: U.S. Department of Defense
The Chinese submarine force, while numerically large, would have an uphill task trying to find U.S. flattops as the real estate to be covered is vast – the Philippine Sea alone is some 5 million square kilometers in area. Indeed, PLAN boats would stand a greater chance of contacting American carriers if Chinese ocean-surveillance capabilities, which have progressed in recent years with the launch of several satellites for this purpose, are harnessed to their full potential. And if a Chinese diesel boat were to locate a U.S. carrier without cueing, the former would find it difficult to continuously track the American vessel’s movement unless the sub’s position relative to the carrier is optimal at first contact. In other words, the SSK, because of its slow speed, is simply in no position to play catch-up with the carrier. After all, both the Kilo and Yuan SSKs have a top submerged speed of around 20 knots and this is for a limited duration only. On the other hand, the Nimitz-class supercarrier and its consorts can make 30 knots or more.
Only the PLAN’s Shangs, with a top speed of some 30 knots, are capable of matching the CSG. The other Chinese SSN in service, the noisy Han, can only make up to 25 knots. Furthermore, Chinese nuclear boats would be caught between a rock and a hard place: Move at slower speeds to reduce detection but risk losing contact with the carrier group, or move faster and risk being discovered. All in all, the “tyranny of geography” could mean that Chinese submarines would find it difficult to establish contact with an American carrier without exogenous elements such as satellite-provided cues. To compound matters, PLAN boats lack towed-array sonar that would enable them to detect targets from a much greater distance compared to hull sonar. In addition, Chinese submariners lack operational proficiency, even though steps like increased patrols have been taken in recent years to remedy this problem.
And if a Chinese submarine were to get into an optimal position relative to an American flattop, can the sub track its target without being detected? The decline of the discipline of anti-submarine warfare (ASW) in the USN since the end of the Cold War does not bode well for this issue. Indeed, James R. Holmes maintains that ASW has been a “subsidiary function (of the USN) for a generation” as a result of the focus on power projection since 1992. The fortunes of the carrier-borne S-3 Viking ASW plane in the post-Cold War period reflect this de-emphasis on ASW. From the 1990s, the aircraft’s main missions shifted to surface warfare and mid-air refueling. In 2009, the Viking was retired altogether, leaving the Seahawk helicopter as the sole carrier-borne ASW platform, and eroding the carrier group’s ASW capabilities. Indeed, hunting subs is merely just one of the Seahawk’s repertoire of missions.
Attacking the Carrier
So assuming a Chinese submarine is able to sneak into position to attack the American carrier, what is the likelihood of its ordnance achieving critical hits? At this juncture, it is appropriate to establish the terms “mission kill” and “platform kill.” Simply put, platform kill occurs when the ship attacked is sunk, while a mission kills involves the ship being unable to perform its primary task(s). The raison d’être of the aircraft carrier is its air wing and the ability to conduct flight operations is indispensable in this aspect. Making its flight deck inoperable would be one way to bring about the mission kill of a carrier. Another would be to reduce the ship’s speed and maneuverability, as it must be able to maintain a steady course and speed for the launch and recovery of aircraft. For America’s adversaries, achieving a mission kill of its carriers might just be enough for a major military and political victory.
The Chinese submarine can attack the American carrier with either its torpedoes or, if it has them, anti-ship cruise missiles (ASCMs). A hit from the former is arguably the more damaging of the two. Indeed, Howarth contends in China’s Rising Sea Power (p. 99.) that “(l)arge armored warships are inherently difficult to sink or disable with hits above the waterline, unless the missiles manage to penetrate a vital area of the ship such as its magazine or combat information center.” Then U.S. Chief of Naval Operations Gary Roughhead took the same line when he maintained in 2011: “I would argue that you can put a ship out of action faster by putting a hole in the bottom [with a torpedo] than by putting a hole in the top.”
A torpedo hit, which is below the waterline, will create a hole in the carrier’s hull and this might slow the ship down and/or make it list. A wake-homing torpedo – a weapon owned by China – is even more dangerous as it tracks the wake created by the target and hits the propeller system or its vicinity upon impact. This is an outcome that would adversely degrade the carrier’s speed and mobility – two factors that affect its ability to conduct flight operations. All in all, attaining torpedo hits on an American carrier has a decent chance of bringing about its mission kill – if the resultant damage is not properly contained.
There have been no instances in the postwar era of American warships being hit by torpedoes. However, there were a few incidents of fires involving USN assets; bearing this in mind, it can perhaps be argued that in any future conflict, the U.S. Navy would be more used to handling hits topside rather than those below the waterline. This is because it would undoubtedly have drawn up a list of “Lessons Learned” after each incident of fire and take appropriate measures in such areas as damage control to be implemented in the future. Although it can also be argued that the USN has had some experience in dealing with hits around the waterline when it handled damage to a number of mined ships in the 1980s and 1990s, it must be emphasized that the mine is a different weapon system together compared to the torpedo. In fact, the largest of these ships mined – the 19,500-tonne USS Tripoli – set off a device containing about 135 kg of explosives and yet its structural integrity was compromised. The amount of explosives in Chinese torpedoes is much higher and the damage these weapons can cause would be significantly higher. To illustrate, the PLAN has the Type 53 torpedo that is with armed a 300 kg warhead. It also has the Type 65 wake-homing torpedo that has a 450 kg warhead. All in all, American ship crew might not be able to handle a torpedo hit as well as one from a missile considering the USN’s lack of experience in dealing with the former; in this light, the submarine-launched torpedo constitutes a genuine threat to the U.S. carrier.
Besides the torpedo, the Chinese submarine can also target the U.S. flattop with ASCMs. China seems to stress the centrality of this weapon in attacking ships. Said an instructor at the Chinese navy’s submarine academy, who wrote a textbook for fire-control personnel: “Under modern combat conditions, the main combat method for attack submarines is to fire anti-ship missiles from underwater to attack enemy surface ships.” However, if this doctrinal emphasis on missiles were to be strictly followed in a war, Chinese submarines might actually be rendered more vulnerable. This is because the launch of a missile under water is inherently a noisy affair – even more so than that of a torpedo – and the resulting “flaming datum” could give away the position of the submarine, making it susceptible to enemy counter-attack. Furthermore, by using ASCMs, PLAN submarines might have a lower chance of hitting and crippling an American carrier.
Modern Chinese boats like the Kilo and Shang have six torpedo tubes each and this means usually a maximum of five ASCMs will be loaded into the tubes and fired. This is because it is typical, indeed prudent, for the submarine to have at least a torpedo loaded and ready for firing in case any sub-surface threat appears. A salvo of a handful of missiles, though dangerous in its own right, hardly constitutes the saturation attack which the Aegis air-defense system on the carrier’s escorts are conceived to handle. That said, coming into service soon are three improved Shangs each armed with a vertical-launch system (VLS) for firing missiles, and this is a development that could significantly complicate the defense of the American CSG. The number of tubes in the improved Shang’s VLS is currently unknown. However if one were to assume a conservative number of eight, that would mean that the boat is capable of launching more than a dozen ASCMs at its target, a troubling development for the U.S. carrier indeed.
The saturation attack where multiple ASCMs are simultaneously fired at a target has been commonly cited as the harbinger of the U.S. carrier’s demise. There has yet to be an instance of such a strike on a warship, so it is difficult to assess whether the attack would overwhelm the CSG’s defense. Nonetheless, the failure of Aegis during the 1988 Flight 655 case and the ineffectiveness of the Phalanx Close-In Weapon System during the 1987 USS Stark incident show that much-touted military technology can disappoint in the heat of battle. It is therefore not inconceivable that the CSG under fire may have to “absorb” a number of missile “leakers.”
There were a number of serious fires involving U.S. flattops in the post-war period and it is reasonable to infer from these blazes what could be the likely aftermath of ASCM hits on a modern carrier. This is because these fires bear a similarity to ASCM hits in that both involve the ship’s topside. The conflagration that engulfed the USS Enterprise in January 1969 is often cited as evidence of the U.S. supercarrier’s ability to take punishment and still remain operational. The fire occurred when nine 500-pound bombs were set off on its flight deck and the explosive power of the blast was said to be equivalent to that of six Russian cruise missiles (Howarth, China’s Rising Sea Power, p. 99.). In spite of heavy casualties – 27 dead and 300 wounded – the catapults and arresting gear of “Big E” remained relatively undamaged, and she resumed flight operations within hours. In other words, the ship sustained the equivalent of half a dozen ASCM hits, without a mission kill. If one were to infer from this case, it could perhaps be said that the ASCM is unlikely to be as effective as a torpedo. However, it must be stressed that this extrapolation does not take into account the fact that at the point of impact, the missile could be moving at supersonic speed. Indeed, the Chinese submarine-launched YJ-18 ASCM has a terminal speed of between Mach 2.5 to 3. The question is thus: “Would the kinetic energy sustained from travelling at such high speeds allow the missile to penetrate the carrier’s armor and hit vital spaces like its magazines?” Witness the sinking of HMS Sheffield during the Falklands War, where a subsonic Exocet penetrated the destroyer’s hull but did not detonate. Nevertheless, the missile caused fires that doomed the ship.
Summing up, the preceding analysis has shown that current PLAN submarines, because of the tyranny of geography and their operational and technological deficiencies, would have considerable difficulty finding and tracking U.S. carriers in the event of a conflict in the western Pacific. However, exogenous elements like targeting information provided by ocean-surveillance satellites could potentially alleviate the shortcoming. And if the Chinese submarine does get to shoot at the U.S. flattop, doing so with torpedoes rather than anti-ship missiles might offer a better chance of mission success.
Going forward, Beijing has always treated the submarine as a key component of its “counter-intervention” strategy against a modern adversary. To this end, the People’s Republic is seriously investing in its undersea fleet, such that it now has more submarines than America has, although their quality is still inferior. As a senior USN official said: “We know they are out experimenting and looking at operating and clearly want to be in this world of advanced submarines.” The key issue is to what extent can the Chinese catch up with the Americans in the realm of undersea warfare? Opines Owen R. Cote perceptively in a 2011 study: “The Chinese are still far from that position, but as in other areas, it would almost certainly be a mistake to assume that they won’t eventually get there if they decide to try.” His words are just as pertinent today. In fact, the case of the Soviet Akula, whose acoustic technologies appeared years before the West believed they would, shows that Washington must never rest on its laurels with respect to Chinese submarines.
To be sure, the United States Navy is cognizant of the threat and has taken steps in recent years to mitigate it. It has, for instance, introduced advanced ASW systems such as the SQQ-89A(V)15 Combat System, the Multi-Functional Towed Array, and the P-8 Poseidon maritime patrol aircraft. Whether or not these and similar measures would enable the U.S. to retain a distinctive edge in the undersea combat realm vis-à-vis China remains to be seen.
Ben Ho Wan Beng is a Senior Analyst with the Military Studies Programme at Singapore’s S. Rajaratnam School of International Studies, and he received his master’s degree in strategic studies from the same institution. Ben has a profound interest in naval affairs, and his works in this area have appeared on The Diplomat, War Is Boring, as well as the Center for International Maritime Security’s Next War blog.