How will new Submarine Sensors and Payloads Influence Naval Warfare in the 21st Century?
Since the beginning of the 20st century, a series of new submarine sensors and payloads have changed naval warfare, sometimes in revolutionary fashion. To a large extent these changes have been cumulative. Changes that first occurred in the First World War are still in place, such as the idea that merchant shipping is inherently vulnerable to attack by torpedo-armed diesel submarines. But increasingly over this period, other new submarine sensors and payloads have not been adopted universally, such as the great strides in passive acoustic sensing that remain a near monopoly of the U.S. Navy, and particularly its submarine force. It is therefore useful to review the history of innovation in submarine sensors and payloads during the 20th century to determine what changes occurred in what navies and where they may still apply. I will discuss four such changes, the last three of which are today largely or completely unique to the U.S. Navy: the torpedo-armed diesel submarine; the quiet, passive acoustic-equipped, nuclear attack submarine; the nuclear ballistic missile submarine; and the conventional land attack cruise missile submarine. After summarizing these four developments I will shift to a discussion of future submarine sensors and payloads and their potential impact.
The development of the torpedo allowed the smallest ships to sink the largest ships, and the marriage of the torpedo with the diesel submarine combined that lethality with a means of operating in distant waters controlled by a superior opponent. This changed naval warfare in WWI by providing the weaker naval power – Germany - with a means of interdicting British commerce even though the German High Seas Fleet had failed utterly to wrest command of the sea from the superior British fleet. In WWII, war came with the German Navy still in the early stages of rearming, causing it to cancel its plans to build a traditional fleet. Instead it focused from the outset on interdicting British commerce using submarines, and arguably came closer to success than in WWI before being decisively defeated in May 1943.
Britain and her allies eventually succeeded in both Battles of the Atlantic by mounting antisubmarine warfare (ASW) efforts that were wildly disproportionate in scale and cost to the submarine threat they were a response to. On the other hand, once the Allied ASW efforts reached maturity, the defeat of German U-Boats in both wars was total.
The U.S. and the Japanese had different experiences with submarines in the Pacific during WWII. Here, there was a more traditional struggle for command of the sea, albeit with fleets using new platforms, including especially the aircraft carrier. But this struggle unfolded in the midst of a very different maritime geography where the respective fleets were separated by the Pacific Ocean rather than concentrated within 500 miles of each other on either side of the North Sea as in WWI. Submarines played a less dominant role than expected in operations against opposing fleets because in blue water diesel submarines were much less effective when used against fast naval combatants than when used in attacks against merchant ships because only in the latter case did the submarine have the speed advantage. In the net, this greatly advantaged the U.S. because only the Japanese were economically dependent on merchant shipping in the way Britain was, while the U.S. remained economically autarkic. Under these circumstances, U.S. submarines shifted to commerce raiding in the western Pacific, while Japanese submarines remained committed to the often fruitless task of finding and attacking American fast carrier task forces in the vast reaches of the central Pacific. Ironically, because of the more constricted seas in which both the Japanese fleet and its merchant marine operated, and cuing provided by Magic, American submarines not only succeeded in completely shutting down Japanese commerce, they also still achieved better results than Japanese submarines in operations against major fleet combatants. Thus, in the Pacific theater, submarines worked decisively to the advantage of the stronger naval power, unlike in the first and second Battles of the Atlantic.
Nuclear power made obsolete the panoply of ultimately successful ASW measures developed in WWII that exploited the diesel submarine’s need to operate mostly on the surface. With nuclear propulsion came the “true” submarine that did not need to surface at all. Nuclear power also provided power densities sufficient to propel submarines at submerged speeds over 30 knots with essentially unlimited endurance, allowing them to run down and attack even the fastest surface combatants. Viewed through the lens of the recently completed world war, the nuclear attack submarine potentially undermined every aspect of American naval power because it would not only threaten the merchant shipping that was central to the U.S.’ emerging postwar alliances, it would also threaten the carrier-based power projection capabilities that had played such a central role in Japan’s defeat. And unlike Germany before either of the two world wars, the Cold War Soviet Navy did not appear distracted by dreams of great ocean-going fleets, embracing a strategy of sea denial rather than control from the outset; but like the U.S. before the two world wars, and unlike Japan and Britain, and in the post war period increasingly the U.S., the USSR was economically autarkic, and thus was not vulnerable to U.S. submarines. All of this could be seen with varying degrees of clarity before USS Nautilus, the first nuclear-powered submarine, went to sea in 1954. Even though the U.S. Navy had pioneered the development of nuclear propulsion, the Soviet Union was shaping up as a peer competitor, and it couldn’t be long before it emulated the U.S. naval nuclear power program, as it did in 1958 with the November. In anticipation of that point, U.S. Navy planners feared that submarines would once again become the weapon of the weaker Navy.
The Third Battle: Innovation in the U.S. Navy’s Silent Cold War Struggle with Soviet Submarines, Newport Paper #16). Thus, submarine versus submarine conflict came to be envisaged as the norm by the U.S. Navy, rather than a rarity, and the acoustic advantages enjoyed by U.S. SSNs against Soviet submarines, including Soviet SSBNs, augured for a highly favorable exchange rate. Thus, despite all expectations, the submarine remained preeminently a weapon of the stronger Navy in the hands of the U.S. during the Cold War, despite the great efforts by the weaker Navy to make it otherwise, and it was the Soviets who ended up on the wrong side of the cost-exchange ratio in the undersea battle.
The next big change in naval warfare caused by a new submarine weapon was muffled by the end of the Cold War. First deployed in 1986, conventional Tomahawk, or TLAM C, was the first long range, precision, land attack weapon. It gave surface ships and submarines a weapon that could penetrate even the most advanced air defenses without any prior suppression effort and strike any non-hardened, fixed target within a ~1000 mile radius with a very high single shot probability of kill (SSPK). In addition, it uniquely gave U.S. submarines a weapon that could be launched from within the periphery of the most advanced anti-access/area denial (A2/AD) network the world has yet seen - as described in the now declassified NIE 11-15 Soviet Naval Strategy and Programs Through the 1990s in March 1983. (See Newport Paper 19 (PDF), Appendix I, pp. 101-184). Precision eliminated the “many weapons, one kill“ syndrome that had plagued air attacks using unguided weapons for decades, nap-of-the-earth flight profiles defeated even the most modern ground-based air defenses by simply eluding them, and submarine basing allowed deployment on platforms that could ignore even the most robust sea denial efforts. Thus, in the mid 1980s, TLAM C did for fixed targets with conventional weapons what Polaris did for fixed targets with nuclear weapons in 1960 – one shot, one kill, no defense. Certainly Tomahawk has been given its due as a transformational weapon given its extensive use since the end of the Cold War, and it was the unique value of its marriage with the submarine that, after much debate and plenty of opposition from within the Navy, led to the decision to convert four Trident SSBNs into SSGNs. But the relative difficulty of this process is an indication of how future changes in naval warfare might be stalled or eschewed altogether.
Future changes in naval warfare have become part of the current discussion about the rise of the Chinese Navy, and particularly its submarine force. For now, the submarine remains the weapon of the stronger Navy in the Pacific. But there are two ways in which this could change: the U.S. could lose its currently massive advantage in ASW, or the U.S. Navy could fail to exploit new submarine sensors and payloads with the potential of causing a fourth major change in naval warfare. Neither of these outcomes need come to pass, but it is arguably less likely that the former will happen than the latter because military organizations generally have an easier time of sustaining existing doctrine in the face of new challenges than they do creating new doctrines.
First, the much touted “death of passive acoustics” at the hands of modern, quiet diesel submarines has proven premature. For example, rapidly deployable passive acoustic surveillance systems exploiting the reliable acoustic path (RAP) are under development by the U.S. which will enable the formation of ASW barriers against even the quietist submarines. Second the maritime geography of a U.S.-Chinese naval competition is more favorable to the dominant naval power than any prior great power naval competition, excepting perhaps that which Britain enjoyed during WWI, and it is certainly better from an ASW perspective than was the U.S. position versus the Soviet Union during the Cold War. (For more on this see Owen R. Cote Jr., Assessing the Undersea Balance Between the U.S. and China (PDF), SSP Working Paper, February 2011) Third, and perhaps most important, the U.S. Navy has an organizational legacy of more than 60 years of intensive and highly successful research and development into methods of detecting submarines, whether to support its own ASW efforts, or in the case of the SSBN security program, to “red team” the ASW methods that might be adopted by its opponents. By contrast, any possible future naval competitor in this realm will be starting from a position of near zero capability or experience. I argue that the biggest variable concerning the future impact of submarines on naval warfare concerns the choices made by the U.S. Navy regarding future submarine sensors and payloads.
The next major change in naval warfare caused by U.S. submarines will likely result from the marriage between the submarine on the one hand, and precision, land attack, tactical ballistic missiles (TBMs) and small, long endurance UAVs on the other.
The systems that form these networks often seek to use the sanctuary provided by mobility in the cluttered environment ashore as a base from which to launch missile strikes against fixed targets necessary for power projection like air bases, or more ambitiously against ships at sea. Ever since the failed “SCUD Hunt” of Desert Storm, persistent airborne surveillance has been identified as key to the rapid identification and precise geo-location of mobile targets, as has been a source of precision weapons for attacking those mobile targets in time urgent fashion when they are found. Everything learned during the decade-long war on terror in operations against IEDs and terrorist leaders has amplified that message. This means that persistent airborne surveillance and time urgent weapons will also need to play a central role in defeating the mobile targets that form the heart of an A2/AD network.
But modern, ground-based air defenses are themselves mobile targets, which introduces a chicken-egg problem at the outset of any anti-A2/AD operation.
At the heart of any DEAD capability against a modern air defense system is the need to destroy relatively small numbers of expensive, phased array engagement radars. Without them, SAM batteries lack the ability to track targets with the accuracy needed to guide missiles against them. These radars need only emit intermittently during an engagement and can be quickly moved afterward. Thus, traditional radar-homing weapons like HARM will not work because they require a continuous signal to home on, and traditional single-platform, angle-of-arrival (AOA) ELINT techniques cannot provide accuracy sufficient to target coordinate-seeking weapons. This challenge first presented itself in Kosovo, albeit for different reasons, and in a much more benign air defense environment; and in different form (COMINT rather than ELINT), this challenge is ubiquitous in the battle against so-called “high value targets” in the war on terror. This has led DOD to embrace an ELINT/COMINT technique long used by the intelligence community that involves time difference of arrival (TDOA) signal processing, whereby a network of at least three platforms surrounding the emitter compares the precise time of arrival of the same signal at three widely separated locations. This enables precise and immediate geo-location sufficient to target coordinate seeking weapons.
TDOA lies at the heart of the Air Force’s current approach to DEAD using the F-16 via the R7 upgrade to the HARM Targeting System (HTS). In its COMINT role in the war on terror, programs like DOD’s net-centric collaborative targeting (NCCT) and the NRO’s real-time regional gateway are using networks of ground-based collectors; legacy airborne platforms like RC-135, U-2s, EP-3s, and Guardrail or UAVs; and COMINT satellites to identify and precisely locate cell phone and push-to-talk radio signals in near real time. In the future, both the U.S. Air Force and Navy plan on using F-35s with such a TDOA capability to accomplish the DEAD mission in an A2/AD environment. This has two consequences: first, it assumes that sea and air bases for these aircraft are available, i.e. a medium as opposed to a high threat environment, or a high threat environment in which some parts of the opponent’s A2/AD system have already been destroyed by other assets; and second, it assumes that the DEAD mission can be accomplished by relatively small numbers of non-persistent assets that come and go to and from the battlefield, providing only an intermittent presence.
A submarine-based DEAD capability would instead hold SAM engagement radars at continuous risk of destruction whenever they emit by operating forward within an A2/AD network’s periphery for as long as needed. This, in turn, would enable two major contributions by the submarine to the Air/Sea battle concept DOD is now contemplating as a counter to A2/AD networks. First, a forward, persistent DEAD threat would enable airborne surveillance platforms like those described above to operate safely just inside the maximum range of their sensors (~150 miles) because a close-in DEAD capability could ensure destruction of engagement radars well before the completion of SAM engagements at such long ranges. Second, given the cueing made available in this way, scarce F-22s and F-35s could efficiently attack other types of mobile targets in the A2/AD network without the prior need to deal with mobile air defenses. (For more on submarine-based DEAD see Owen R. Cote Jr., Submarines in the Air Sea Battle (PDF), JHU/APL Submarine Technology Symposium 2010)
There are certainly other innovations in submarine sensors and payloads to imagine, and indeed some may already be under development, but there is a strong logic behind U.S. submarines acquiring a DEAD capability against mobile air defenses. Ever since the submarine first threatened to provide a weaker Navy the ability to overthrow a stronger Navy’s command of the seas, the dominant Navies have been forced to respond vigorously to this threat. During the first half of the 20th century, these responses were often slow in coming, asset intensive and expensive compared to the threat they were countering, and therefore prone to abandonment in peacetime. In the second half of the 20th century, a different dynamic emerged. Peacetime technological and doctrinal innovation combined to make the submarine a tool that favored the dominant naval power during the Cold War, both because the submarine became a dominant part of the ASW solution, and because it acquired the ability to project power ashore against fixed targets without the need to first defeat an opposing A2/AD network. Today, the dominant naval power faces a different A2/AD threat than the one it faced during the Cold War, one in which mobile targets ashore play a dominant role. U.S. submarines can play a role in meeting that threat only with new sensors and payloads that go beyond the legacy of the last one.