Combined Arms Support to Submarine Operations

Last month in the conclusion to my series examining the Jeune École, I noted that Germany’s use of submarines in the Atlantic for theater denial and Guerre de Course during the two World Wars—while incredibly costly to the Allies in terms of blood and treasure—ultimately failed in large part because German surface combatants and land-based aircraft could not seriously offset Allied anti-submarine efforts.

German U-boats were on their own in the Atlantic during the First World War because their surface combatant brethren could not break through the Royal Navy’s North Sea blockade in numbers. Granted, a handful of German large and medium surface combatants were forward deployed when the war broke out, and a few Germany-based medium surface combatants and armed auxiliaries managed to access the Atlantic at various points over the war’s course. All of these warships, though, operated as commerce-raiders either by design or by default—and few managed to operate for longer than a handful of months before being neutralized. Allied anti-submarine forces, whether operating independently or (after April 1917) as convoy escorts, therefore only had to contend with their prey

Nor did U-boats receive substantive support from the Kriegsmarine’s surface forces during the Second World War. If anything, Germany was at an even steeper surface order of battle deficit relative to the Royal Navy than had been the case two decades earlier. As a result, and with the exception of the April-June 1940 Norwegian campaign, the Kriegsmarine once again principally used its larger surface combatants for commerce-raiding. Although the Kriegsmarine’s surface threat to Britain’s lines of communication with the Americas was peacemeal and limited to 1939-1941, the threat it posed to the allies’ lines to the Soviet Union through the Norwegian Sea was more serious and lasted until 1943. One could make the case that the Kriegsmarine’s large surface combatants based in Norway supported U-boats in the case of convoy PQ-17, but that stemmed from the British Admiralty erroneously ordering the convoy’s ships to scatter to their fates in the belief that German surface raiders including the Tirpitz were approaching (they were not). In any case, the sad story of PQ-17 was not repeated.

The advent of theater-range aircraft during the interwar years, however, meant that U-boats did receive some combined arms support. Specialized Luftwaffe bombers were fielded to provide surveillance and reconnaissance support to Kriegsmarine surface and submarine units. These bombers also conducted anti-ship raids of their own. The Luftwaffe was able to iteratively increase its oceanic reach throughout the war, established a dedicated command for maritime operations in the northeastern Atlantic, and introduced radio-controlled anti-ship weapons that permitted standoff attacks. The first combat use of one of these weapons, in fact, caused the allies to temporarily halt offensive anti-submarine Surface Action Group (SAG) operations in the Bay of Biscay; this provided U-boats based on the French Atlantic coast with a temporary window of opportunity for safer transits to and from the open ocean.

And yet, the Luftwaffe never operated enough aircraft to pose a persistent threat to allied convoys or offensive anti-submarine SAGs. Moreover, the Luftwaffe and Kriegsmarine never hammered out doctrine, communications protocols, or planning processes that could enable effective operational coordination. On-scene tactical coordination between aircraft and U-boats was sporadic; the occasional noteworthy successes that did occur did not translate into major campaign gains. Luftwaffe land-attack raids against major British ports, naval bases, and shipbuilding hubs to suppress convoy and SAG operations as well as new ship construction were sustained for only the first half of 1941, were largely ineffective in their operational purpose, and were ultimately discontinued. Most significantly, U-boats operating in the western and southern Atlantic were outside the Luftwaffe’s range—and thus were on their own.

The Soviet Union’s leading maritime strategist of the Cold War, Fleet Admiral Sergei Gorshkov, took note of all this. In his 1976 book The Sea Power of the State, Gorshkov observed that Germany’s Second World War U-boat operations ultimately failed to achieve their strategic objectives in part because they

“…did not have the support of other forces, notably, aircraft, which could have been an irreplaceable means of reconnaissance, to fulfill the tasks of destroying anti-submarine forces and also to act against the economy of the opponent, particularly his shipbuilding industry, and to inflict blows on cargo ships in the ocean.” (Pg 120)

Gorshkov then observed that while German U-boat operations were representative of the roles submarines should play in war, the Germans erred as

“Throughout the war not a single attempt was made to counter the anti-submarine forces of the Allies in an organized way from operating with total impunity.” (Pg 120-121)

Notwithstanding the irony that Soviet interests in the war were on the receiving end of the U-boat operations he lauded, Gorshkov appeared to be arguing that Soviet attack submarines should perform much the same roles in a notional conflict with the U.S. and NATO. He further seemed to argue that Soviet air forces should provide his submarines with the direct and indirect forms of support that he had outlined.

Whatever Gorshkov may have actually believed, his Navy’s planned use of submarines for barrier protection of the Soviet maritime periphery represented the polar opposite of what his book seemed to recommend. Part of this was due to the paramount Soviet military-strategic task of protecting the motherland from naval strikes, whether conventional or nuclear. Part of this was also due to Soviet leaders’ fears that their strategic nuclear reserve force—their SSBNs—might be subjected to wartime attrition via U.S. and NATO conventional offensive anti-submarine operations. If the U.S. and NATO could attain a superior ‘correlation of nuclear forces’ during the conventional fight, Soviet logic went, then the West would gain a major card to play in the bargaining over war termination. Soviet Naval Aviation, surface forces, and attack submarines were consequently tasked with preventing U.S. and NATO naval forces from attacking the SSBNs; comparatively few Soviet attack submarines were to be hurled at NATO’s trans-Atlantic lines of communication at the beginning of a war.

It follows that offensive strategic anti-submarine warfare was one of the primary reasons the 1980s U.S. Maritime Strategy emphasized forward operations within the Soviet oceanic periphery. The strategy suggested that if U.S. carrier battleforces in the Norwegian Sea and Northwest Pacific could weather or outright defeat Soviet anti-carrier forces’ onslaught early in a war, then U.S. and allied anti-submarine forces might gain more operational freedom to interdict older Soviet SSBNs (or any Soviet SSNs for that matter) attempting to break out through forward geographic chokepoints into the ‘world ocean.’ Moreover, U.S. naval airpower could also be theoretically used to suppress Soviet surface and airborne anti-submarine forces protecting the newer Soviet SSBNs’ bastion patrol boxes. If these Soviet anti-submarine forces could be suppressed, then U.S. and NATO SSNs operating against the bastions (or conducting land-attack cruise missile strikes into the Soviet Union, if so ordered) would only face opposition from their acoustically-inferior Soviet counterparts. In essence, the 1980s Maritime Strategy redirected Gorshkov’s logic regarding combined arms support of submarine operations against his own fleet.

The late Cold War is not the only example of U.S. combined arms support of submarine operations. Again, as I noted in my Jeune École series’ finale, U.S. offensive submarine operations against Japanese sea lines of communication during the Second World War benefitted indirectly from the Imperial Japanese Navy’s myopic fixation on fleet-on-fleet operations:

The U.S. Navy fast carrier task force’s advance across the Pacific arguably provided increasing amounts of indirect combined arms support to their submariner brethren over time by occupying the attention of Japanese naval resources that theoretically could have been assigned to convoy defenses or submarine-hunting groups. Although the Imperial Japanese Navy showed little interest in protecting convoys from submarines during the war, an absence of the U.S. Navy carrier threat in the Central Pacific after 1942 might have provided room for reallocating some Japanese fleet assets to anti-submarine tasks as Japanese merchant vessel losses mounted.

So what might these history lessons mean for future U.S. Navy doctrine and operating concepts?

For starters, it’s important to keep in mind that a submarine’s combat “invisibility” has never been absolute. If a submarine torpedoes a ship, then the other side’s anti-submarine forces gain a “flaming datum” to orient their search. If a submarine launches a missile or raises a periscope/ESM mast for too long within the other side’s effective radar (or visual) coverage and is detected, then the other side's hunters know precisely where to start their cordon and redetection efforts—or place quick-response weapons in the water. A submarine may be able to scan or shoot far enough away from an opponent’s anti-submarine aircraft or surface combatants to be able to “break datum” before the hunters can react effectively, but it cannot count on that favorable scenario always being available. And the closer a submarine operates to an adversary’s coast, the denser the coverage by the adversary’s anti-submarine sensors (whether seabed-mounted sonar arrays, ship and aircraft-mounted sonars/radars, or fishermen’s eyes) and platforms will be. These assets might not be able to find or shoot at the submarine, but their presence might unnecessarily complicate its mission. In some situations it might even delay or prevent the submarine from completing that mission.

In a major modern war, U.S. SSNs and SSGNs would be tasked with land-attack strikes, special forces insertion/extraction, and intelligence/surveillance/reconnaissance collection within a contested zone’s inner reaches. The SSNs would additionally be tasked with forward anti-submarine and anti-surface operations. Just as was the case in the 1980s Maritime Strategy, our submarines might situationally benefit from some external help from other U.S. or allied forces in suppressing the adversary’s ability to conduct effective anti-submarine operations.

This help might take the form of aircraft performing anti-ship missile raids against enemy anti-submarine SAGs inside a contested zone. It might take the form of offensive sweeps by fighters against the adversary’s maritime patrol aircraft. The mere fact that adversary anti-submarine forces were attacked in a particular area in a particular way might induce the adversary to limit or cease operations in that area while it figures out how to adapt; this could be exploited to great effect by U.S. submarines even if the ‘pause’ only lasted for a few days.

External forces might also provide submarines with deception and concealment support. This might consist of air or surface naval operations that have the primary or secondary purpose of distracting the adversary’s attention from a U.S. submarine’s operating area. Or perhaps air or surface forces might release submarine-simulating unmanned underwater systems at some standoff distance from the adversary’s coast; these decoys could then “swim” forward into designated areas to confuse or distract the adversary’s anti-submarine forces.

External support to forward submarine operations might additionally include surveillance and reconnaissance aircraft that report their surface pictures via interior lines of networking to a higher-echelon commander. The commander could then broadcast that information along with theater or national-level naval intelligence information “in the blind” for our submarines to receive and use for their purposes.

If authorized by U.S. political leadership, combined arms support to our submarines might even take the form of U.S. cruise missile strikes against the adversary’s naval and air bases supporting anti-submarine operations. As I’ve noted previously, it must be understood that a U.S. President’s decision-making on this question would be heavily—and perhaps decisively—affected by the escalatory precedents already set by the adversary (regardless of who that might be) in the conflict. 

These forms of external support would not be possible to all U.S. forward submarine operations due to asset availabilities. Nevertheless, air or surface operations could be sequenced or coordinated to support specifically prioritized submarine operations or operational periods.

The adversary’s ability to pose an excessively high threat to U.S./allied air or surface operations within a contested zone’s inner sections would also be a major limiting factor. Special assets such as very low observable aircraft might be needed to conduct attacks in support of submarine operations—or cue attacks by other forces armed with long-range weapons. These penetrating aircraft in turn might need to be supported via submarine-launched land-attack cruise missile strikes against an adversary’s wide-area air surveillance sensors or air defense systems. This is a great example of why mutual support between combat arms is so critical in modern warfare. Even so, it is quite likely that the further forward a submarine operates within a contested zone, the more likely external support (if any is possible) will be indirect.

None of this changes the fact that U.S. submarines will assuredly conduct high-risk independent operations deep within an adversary’s maritime periphery in a notional major war. That’s been a constant from the Second World War, through the Cold War, to today. U.S. direct and indirect support of submarine operations has also been a constant, whether it was inadvertent as in the Second World War or consciously planned for as in the 1980s Maritime Strategy. I’d argue that external combined arms support (as possible and relevant) can have much to offer our submarines in the present and future as well.

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I'll be on hiatus next week. I aim to resume posting the week of August 10th.

The views expressed herein are solely those of the author and are presented in his personal capacity. They do not reflect the official positions of Systems Planning and Analysis, and to the author’s knowledge do not reflect the policies or positions of the U.S. Department of Defense, any U.S. armed service, or any other U.S. Government agency.

Sea Lanes Protection Between the First and Second Island Chains in a Notional Sino-American War

On Tuesday, I summarized China’s potential wartime anti-ship capabilities between the First and Second Island Chains. It stands to reason that the U.S. and allied ability to avoid or parry any PLA attacks in these waters would depend upon the margin of temporary localized maritime superiority—or sea control, if you will—that could be extended around a transiting convoy, replenishment group, or naval battleforce.[i] This margin would likely be highest in the waters that could be persistently covered by fighters, Airborne Early Warning (AEW) aircraft, and wide-area anti-submarine aircraft operating from the Marianas, Japanese home islands, or the central/southern Philippines.

As this sea control coverage thinned out with range, PLA forces would in theory gain more operational flexibility. This might be offset, however, through the intelligent use of the one or two U.S. Navy aircraft carriers available in theater during a war’s opening weeks. I’ve previously noted how these carriers ought to be used to provide situation-dependent sea control support to Surface Action Groups (SAG) operating further forward, and alluded to their utility in providing situation-dependent tactical support to defenders in embattled First Island Chain territories like the Ryukyus. The positioning required for those tasks could also allow their fighters and AEW aircraft to screen CLF groups, military sealift convoys, and prioritized commercial vessels transiting outside effective land-based air coverage. With two carriers working together, it might even be possible to occasionally use actual or simulated shipping as ‘bait’ for luring Chinese strike aircraft raids into aerial ambushes.

It additionally should be noted that the U.S. and allied ability to delay or prevent the Chinese Ocean Surveillance System (COSS) from locating and correctly classifying transiting ships would severely complicate the PLA’s ability to cue effective anti-ship attacks. Emissions control, operational and tactical deception, and physical as well as electronic attacks against COSS assets would be essential aspects of any U.S. and allied sea lanes protection campaign. Emissions control and tactical deception would also greatly complicate PLA strike aircraft and submarines’ job of locating, correctly classifying, and targeting protected shipping. The use of “decoy groups,” perhaps using a mix of unmanned systems and actual manned low campaign-value platforms that together simulated a convoy or naval battleforce, might induce PLA attackers to waste precious time and weapons inventories engaging false targets. Better yet, it might cause them to move out of positions from which they could detect and intercept actual shipping. Attacking decoys would be particularly harmful to PLAN submarines, as every weapon wasted (and in the case of AIP boats, fuel burned moving into attack position and then "breaking datum") would eat into the amount of time the boat could remain on patrol before needing to head home for replenishment, and the time spent "breaking datum" would be time the boat would not be able to hunt effectively. Effective deception and concealment would likely have detrimental psychological effects on PLAAF and PLAN crews; over time these effects might become debilitating—and highly exploitable by U.S. and allied forces in their own right.

Lastly, U.S. political leadership might opt to selectively strike PLAAF airbases, PLAN submarine bases, and related PLA infrastructure on the Chinese mainland with long-range guided munitions in order to suppress PLA operational tempo. This would be especially likely if the PLA had set the escalation precedent of striking allied territories first at the opening of the war. Such strikes would have to be highly bounded and selective in terms of their targets in order to mitigate escalation risks. U.S. Navy submarines and U.S. Air Force intercontinental-range strike aircraft would probably perform these strikes, with additional strikes launched from Aegis combatants operating as offensive SAGs. Reducing the PLA’s ability to cycle anti-ship attackers into the Western Pacific would be of immeasurable help to the sea lanes protection effort.

With all these combined arms contributions in mind, the principal screening challenge from a surface combatant standpoint would be defending convoys and CLF ships against “leaker” anti-ship missiles fired by PLA strike aircraft and "pop-up” missile or torpedo attacks by PLAN submarines. The density of the PLA threat in a given area arguably would determine an escort’s necessary capabilities. Aegis combatants’ area air defense capabilities would probably be highly desirable for escort missions in the vicinity of the Ryukyus, Taiwan, and Luzon given the proximity to the Chinese mainland. It’s important to remember, though, that the U.S. only has nine Aegis combatants permanently homeported in Japan (with two more coming by 2017), and these warships would probably be charged with escorting the Navy’s Japan-homeported carrier, protecting the Navy’s Japan-homeported amphibious warships, executing offensive SAG missions, and performing ballistic missile defense tasks. The Navy has thirty-eight other Aegis combatants homeported in the Pacific, eleven of which are homeported in Pearl Harbor. However, not all would be surgeable due to the inter-deployment maintenance and training cycle (and this says nothing of the surge-readiness impacts stemming from the 2011 Budget Control Act). We might theorize that of the five West Coast-based carrier battleforces, the first might already be forward deployed in or near the Western Pacific as a crisis peaked, the second and third might be surgeable for arrival forward within 30 days, the fourth might be surgeable within 90 days, and the fifth would have to complete its ships’ (abbreviated) overhauls and pre-deployment workups before surging. Some of these Aegis combatants would not be detachable from their carrier battleforces, and those that were detachable might be needed more for offensive SAG operations.

Not all of the Aegis combatants would necessarily deploy with carriers, though. If we assume that two-thirds of the Pearl Harbor contingent surged as a crisis peaked, we might have seven Aegis combatants available for tasking along the First Island Chain. These warships would be well-placed for protecting shipping to the Ryukyus, Luzon, or eastern Taiwan. Even so, their use for these missions would trade against their use in offensive SAG operations.

The story would be similar with respect to the Japan Maritime Self-Defense Force’s (JMSDF) Aegis contingent. Japan fields six Aegis DDGs and plans to build two more by 2020. Nevertheless, their principal mission of homeland ballistic missile defense would prevent some number of them from performing sea lanes defense operations. The South Korean Navy’s three Aegis DDGs are not counted in this analysis as it is unlikely they would be offered up for operations that did not involve direct defense of their country’s sea lanes.

It should be clear that Aegis combatants’ use for direct protection of shipping would trade against a large number of other high-priority missions. Moreover, Aegis combatants would generally be tethered to the western half of the waters between the two island chain lines. This would hardly preclude their use for sea lanes and CLF protection, for example as a forward screening layer by virtue of their positions, but they probably wouldn’t be able to closely escort shipping all the way from port to port.

Therein lies the logic of a small surface combatant possessing medium-range anti-air and anti-submarine capabilities. Such a combatant would be entirely sufficient for close escort within waters in which air defense is provided by friendly AEW and fighter aircraft supported by aerial refueling aircraft. Closer to the Ryukyus-Taiwan-Luzon line, this kind of combatant would backstop Aegis combatants’ defensive coverage of a convoy.

The proposed LCS-derived frigate will possess the towed active and passive sonar arrays as well as helicopter capabilities needed for effective anti-submarine warfare. CSBA’s Bryan Clark has also outlined how it could receive the requisite anti-air capabilities for shipping escort.[ii] These improvements would not allow the LCS-derived frigate to detect a submarine-launched sea-skimming anti-ship cruise missile raid beyond effective shipboard radar coverage, though. Land or sea-based AEW support via the Navy Integrated Fire Control-Counter Air capability would be crucial to that end.

Bryan has additionally proposed a longer-range shipboard anti-submarine missile than the legacy Vertical Launch Anti-Submarine Rocket; such a weapon could be very effective in disrupting a PLAN submarine’s attack preparations.[iii] It’s worth pointing out that if COSS could not provide a PLAN submarine with a targeting-quality tactical picture to support firing anti-ship cruise missiles from over-the-horizon, the PLAN submarine would have to close within the range of its onboard sensors. If we assume the primary use of sonar for this purpose, that range might be one to two convergence zones from a target (perhaps 30 nautical miles in the first case and 60 nautical miles in the second case). A shipboard “rocket-thrown torpedo” able to quickly reach out to the first convergence zone and ideally also the second would thus be highly useful.

It’s important to note that the JMSDF already fields two light destroyer/heavy frigate classes that would anchor shipping protection in the approaches to the Japanese home islands and Ryukyus.[iv] As I noted earlier, though, there might not be enough of them to fully carry the shipping escort load within the waters Japan was primarily responsible for protecting. This suggests the utility of the LCS-derived frigate gaining medium-range anti-air capabilities.

One final point is that there would be a demand for LCS-derived frigates to participate in offensive SAGs. It would accordingly be desirable to backfit as much of the LCS-derived frigates’ anti-surface and anti-submarine capabilities as possible into legacy LCS hulls in order to free up as many of the frigates as possible for shipping protection tasks. The logic for using backfit LCSs instead of the frigates in forward-operating SAGs is simple: since the frigates are not presently slotted to receive medium-range air defense capabilities, and since Aegis combatants would be principally responsible for SAG air defense anyway, then the inclusion of backfit-improved LCSs instead of air defense-capable frigates in the SAGs would not alter the existing concept of operations.

The bottom line is that protection of shipping, including the CLF, would likely be far more resource-intensive than is often assumed in the strategy debates. Sea lanes protection would be absolutely critical to the U.S. prevailing in the war, and as such merits extensive study and analysis. I will note that I have never participated in campaign analysis of these questions, nor have I ever been “read into” any such analyses that might have been conducted. Detailed quantitative analysis may very well prove that some of my key assumptions and conclusions are incorrect. Even so, my errors almost certainly center on the specifics of the threat and not on its general nature or the needed seriousness of the offsetting response.

The views expressed herein are solely those of the author and are presented in his personal capacity. They do not reflect the official positions of Systems Planning and Analysis, and to the author’s knowledge do not reflect the policies or positions of the U.S. Department of Defense, any U.S. armed service, or any other U.S. Government agency.

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[i] The discussion that follows is heavily influenced by CAPT William J. Toti, USN (Retired). “The Hunt for Full-Spectrum ASW.” Naval Institute Proceedings 140, No. 6, June 2014. Toti’s article is seminal on modern anti-submarine warfare and should be read in its entirety in parallel to this post.

[ii] See Bryan Clark. “Commanding the Seas: A Plan to Reinvigorate U.S. Navy Surface Warfare.” (Washington, D.C., Center for Strategic and Budgetary Assessments, 2014), 27, 50-51.

[iii] Ibid; 27.

[iv] A third similarly-capable JMSDF destroyer class exists but would generally be tied to providing air defense support to Kongo-class DDGs on ballistic missile defense patrols.

Potential Chinese Anti-Ship Capabilities Between the First and Second Island Chains

Chinese Active Defense Layers (Office of Naval Intelligence graphic). Note that the range lines reflect where PLA aircraft and submarines might be expected to operate in wartime based on evidence to date. While PLA aircraft would be unlikely to fly further east from the second layer's line if U.S. and allied air coverage from bases along the Second Island Chain was strong, the same might not be true for PLAN SSNs. Also note that the maritime approaches to Luzon and the northern/central Ryukyus fall within the PLA's middle layer, and Taiwan and the southern Ryukyus within the inner layer.

There was a pretty lively debate in the comments to Chris Mclachlan’s post last month about the Combat Logistics Force. No one took issue with his observations that the CLF might be undersized for sustaining high-tempo forward U.S. Navy operations in the event of a major Sino-American war. Nor did anyone contest his argument that our replenishment ships lack the basic self-defense capabilities their Cold War-era predecessors carried. Instead, the debate focused on Chris’s assertion that CLF ships ought to be escorted during wartime by a small trans-oceanic surface combatant possessing medium-range anti-air and anti-submarine capabilities.

Needless to say, I agree with Chris’s view. Such an escort would be a necessary part of the overall combined arms solution set to protecting not only CLF assets but also the shipping that would surge reinforcements and materiel to embattled U.S. allies in East Asia, provide steady logistical sustainment to the U.S. and allied forces deployed to or based in those countries, and maintain the flow of vital maritime commerce to and from those countries. One rarely sees any of these four critical tasks acknowledged in discussions within the security studies community. I believe that represents a dangerous analytical oversight, as an American failure to adequately protect its own and its allies’ sea lines of communications in a war with China would be strategically disastrous. In today's post, I'm going to outline China's ability to threaten these lines in a notional major war. On Thursday, I'll outline how the U.S. and its allies might offset that threat.

Let’s first look at the strategic geography of the problem. The sea lanes in question pass through the waters between the First Island Chain and the line stretching from Hokkaido through the Bonins and Marianas to the Palaus (e.g,  the “Second Island Chain”). I’ve recently written about the PLAAF’s effective reach into the Western Pacific, and it’s been widely understood for years that late-generation PLAN submarines possess the technological capability to operate for several weeks in these waters before having to return to port. China would be hard-pressed to achieve localized sea control anywhere within this broad area; its own surface combatants and shipping would be just as vulnerable to attack. It wouldn’t need sea control, though, to achieve its probable campaign-level objectives of bogging down (or outright thwarting) an effective U.S. military response, or perhaps inflicting coercive economic pain upon one or more embattled American allies. The use of PLA submarines and strike aircraft to pressure U.S. and allied sea lines of communications would be entirely sufficient. And as Toshi Yoshihara and Martin Murphy point out in their article in the Summer ‘15 Naval War College Review, these kinds of PLA operations would be consistent with the Mao-derived maritime strategic theory of “sabotage warfare at sea,” albeit at a much greater distance from China’s shores than the theory originally conceived. Such operations have been widely discussed in Chinese strategic literature over the past two decades.[i]

It bears noting that our East Asian treaty allies like Japan, South Korea, and the Philippines would have inherent roles and responsibilities defending their sea lines of communication. Nevertheless, they probably would not be able to fulfill the mission entirely on their own given their maritime forces’ sizes and capabilities. There would probably need to be a geographical line of responsibility similar to what the U.S. and Great Britain worked out in the Atlantic during the Second World War; shipping protection west of the line would primarily be the ally’s responsibility, and the U.S. would be primarily responsible for shipping protection east of the line. Even so, the U.S. would probably still need to contribute escorts and supporting forces to assist the ally in protecting sea lanes that were within some threshold distance of the Chinese mainland. Shipping protection in the approaches to the Ryukyus, Taiwan, or western Luzon particularly come to mind.

While it is true that U.S. and allied forces could probably pressure the PLA’s ability to push submarines and aircraft through the Ryukyus’ various straits or the Luzon Strait in a war, they would probably not be able to fully seal those doors—at least not during the conflict’s early phases. The biggest reason for this would be the straits’ sheer proximity to the Chinese mainland: PLAAF/PLAN fighters would be readily able to escort their strike aircraft brethren out into the Western Pacific and back, not to mention threaten any U.S. or allied anti-submarine aircraft or surface combatants patrolling the straits. Granted, Chinese fighters would be exposed to any sea-based and mobile land-based area air defense systems covering the straits and their approaches. They might also be confronted by U.S. or allied fighters operating from austere island bases in the vicinity of the straits, or from aircraft carriers or land bases located at various distances “over the horizon” to the east. U.S. and allied defenders could additionally use any number of countertargeting tactics to reduce their susceptibility to attack.

However, even if the PLA could not damage or destroy many of these forces per raid, it could still take actions that effectively suppressed the straits “guardians.” One tactic might be to salvo land-attack or anti-radar missiles to distract the defenders or induce them to keep their “heads down” shortly before or during a straits transit. Another might be to damage runways or austere airstrips as possible in order to constrain the defenders’ air operations; repairs could take precious hours. Electronic attacks and tactical deception could also be used to screen transiting PLA aircraft and submarines. Periodic PLA suppression raids would neither be small undertakings nor without risk to the forces performing them, but they might be sustainable on an as-needed operational tempo for several weeks or months at minimum.

The other factor that would make it impossible to hermetically seal the First Island Chain barrier would be the difficulty in maintaining persistent U.S. or allied submarine coverage in all of the requisite straits. The U.S. presently has thirty-one non-special-purpose SSNs stationed in the Pacific; three are homeported in Guam and twenty in Pearl Harbor. Only a small number would be deployed at sea within quick steaming of the straits, though, unless timely indications and warning of an impending crisis or conflict were received and then acted upon by U.S. leaders. The high-readiness Guam boats would be able to arrive on scene fairly rapidly once sortied, but it would take several more days for them to be reinforced by Pearl Harbor boats—not all of which might be immediately surgeable due to inter-deployment maintenance. Japan could surely contribute a number of its sixteen modern SSs in active service, but again not all of them might be surge-ready at any given time. And while the U.S. and Japanese fleets will be receiving additional boats over the coming decade, it will not be at a rate and scale that would dramatically change the straits coverage math. Hypothetical seabed-mounted sonar arrays in these straits or their approaches might help improve these odds by cueing available U.S. or allied submarines (or other anti-submarine forces) to a PLA submarine transit. The probability of a friendly submarine intercepting a PLA submarine detected this way, though, would depend upon the time between when the cue was broadcast and when it was received by the friendly sub, how the friendly sub's effective sonar ranges in those waters affected its ability to redetect the trespasser, and whether the friendly sub could cover the distance from its starting point to have a chance at redetection before the cueing data "aged out." More than one boat might be required to cover any particular strait with a certain margin of confidence; this would be especially true for the wider straits. Nor would anti-submarine patrols in the straits be the two sub fleets’ sole mission at the beginning of a major war: there would be equal if not greater demands for land-attack strikes, anti-submarine and anti-surface patrols inside the First Island Chain, anti-submarine patrols between the two island chain lines, special forces insertion/extraction, and far-forward intelligence/surveillance/reconnaissance. U.S. and Japanese submarine coverage of the straits simply could not be absolute.

It would be excellent if U.S. and allied forces could attrite the PLA forces making or supporting straits transits by a few percent each time without suffering equivalent attrition; the cumulative effects on the PLA’s overall warmaking capacity would be significant. But it would take weeks if not months for those effects to really show. That’s why the ability to logistically sustain the land-based forces waging the protracted frontline fight would be so crucial to U.S. war strategy. If the PLA were to inflict enough pressure on these logistical flows, the barrier defense would eventually wither on the vine.

It’s also important to remember that this imperfect barrier would only function in an open war—not during a crisis. Any PLAN submarines sortied prior to the outbreak of open hostilities could in theory patrol between the two island chain lines for campaign-significant amounts of time before having to hazard a trip back through the First Island Chain gauntlet. Modern PLAN SSNs like the Type 093 and its Type 095 follow-on would have an obvious endurance advantage over Air-Independent Propulsion (AIP) boats like the Type 041, but even the latter could probably remain underway for a few weeks before requiring a return to port. During that time, the mere fact that PLAN submarines were unlocated in the Western Pacific would undoubtedly affect U.S. operations (and tempo) in theater. The Royal Navy’s experience coping with a single unlocated Argentine submarine during the Falklands War is instructive on that point.

It would not take many PLAN submarines to generate such effects. For instance, let’s assume that the PLAN allocated its Type 041s, Type 093s, and Type 095s for war-opening operations between the two island chain lines while simultaneously holding its Type 035A/B/G, Type 039, and Kilo-class diesel-electric boats back for operations within the East and South China Seas. Let’s also assume China had its planned twenty Type 041s and five Type 093s in commission, plus perhaps five Type 095s as well, when a conflict erupted. Lastly, let’s assume that these boats’ material conditions of readiness were high enough to sortie two-thirds of them into the Western Pacific as the crisis phase peaked. Thirteen AIP boats and six SSNs might not seem like a lot within such a broad expanse. However, as Julian Corbett pointed out a century ago, the most “fertile” areas for hunting ships are “the terminals of departure and destination where trade tends to be crowded, and in a secondary degree the focal points where, owing to the conformation of the land, trade tends to converge.”[ii] If the PLAN followed Corbett’s logic, it might position its submarines in waters the U.S. and its allies would have to traverse to access (or break out of) selected major ports along the First Island Chain during the war’s first weeks. Or it might assign those duties to the Type 041s and deploy its SSNs in the waters just west of the Marianas that shipping from Guam, Hawaii, or the continental U.S. might seek to traverse. Or if the Chinese Ocean Surveillance System’s (COSS) coverage between the island chain lines remained adequate after the war started, China might try to steer its SSNs into mid-transit contact with U.S. or allied shipping.[iii] What’s more, the lingering effects of a PLA conventional first strike against major U.S. and Japanese bases in the Japanese home islands and Okinawa, subsequent PLA suppression operations against U.S. or allied straits-guarding forces along the Ryukyus-Luzon line, and in-theater U.S. and allied anti-submarine-capable forces’ sheer combat load prior to the arrival of reinforcements from the U.S. suggest that at least some PLAN submarines could complete at least one full cycle from their patrol areas to port for replenishment and then back into the Western Pacific before the “happy time” window began to close. This would especially be true for PLAN submarines patrolling the approaches to the Ryukyus, Taiwan, or Luzon.

Add the PLAAF/PLAN strike aircraft threat back into the mix and it should be apparent that U.S. and allied use of the Western Pacific’s surface between the two island chain lines would likely be opposed early in a notional war. The key variables driving China’s anti-shipping potential within these waters would be COSS’s ability to provide PLA aircraft and submarines with actionable targeting cues despite intense U.S. (and possibly allied) efforts to degrade and deceive this system-of-systems, the PLA’s ability to push those forces through contested First Island Chain straits when and where needed, and the operational range and endurance of those forces. 

The views expressed herein are solely those of the author and are presented in his personal capacity. They do not reflect the official positions of Systems Planning and Analysis, and to the author’s knowledge do not reflect the policies or positions of the U.S. Department of Defense, any U.S. armed service, or any other U.S. Government agency.

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[i] For instance, see Chapter 3 of Roger Cliff, et al. “Entering the Dragon’s Lair: Chinese Antiaccess Strategies and Their Implications for the United States.” (Santa Monica, CA: RAND Corporation, 2007).

[ii] Julian Corbett. Principles of Maritime Strategy. (Mineola, NY: Dover Publications, 2004), 263.

[iii] For more detail on COSS, see Section 2 of Jonathan F. Solomon. “Defending the Fleet from China’s Anti-ship Ballistic Missile: Naval Deception’s Roles in Sea-Based Missile Defense.” (Master’s Thesis, Georgetown University, 2011).