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24 July 2021

Unmanned Ships and the Future of Deterrence

James Wirtz

Although the origins of contemporary naval strategy are often shrouded in the mists of time, the notion of a “bimodal” Navy, whereby the fleet is divided into one force specializing in sea control and the other in sea denial, can be traced to a 2007 article published by retired Navy Captain Wayne Hughes in the Naval War College Review. In his essay, Hughes mostly concentrated on explaining how the U.S. Navy contributed to the Cold War strategy of containment; nevertheless, his analysis eventually turned to the prospect of great power competition looming on the strategic horizon and what that competition would mean for the fleet:

The existing Navy comprises large, efficient ships to project power ashore, principally in the form of air strikes, missiles, and Marine Corps elements. Against China, the need to threaten air and missile strikes will not change, but China has developed the means to attack large ships at sea. The Navy must now explore building a more distributed fleet that is offensively disposed yet can suffer losses and fight on, for no defense at sea can be perfect against a skilled opponent.1

Hughes suggested that not only budgetary considerations, but also the physics governing the behavior of floating objects had driven the Navy to pack ever more capability into a shrinking number of large vessels, placing “too many eggs in too few baskets,” so to speak. This was fine in a permissive environment in which the Navy faced few threats, allowing it to project power ashore with relative impunity. If those same ships faced a credible threat, however, even the loss of a few vessels would represent an alarmingly high reduction of U.S. naval capability, especially because only a few warships are operating forward at any given time. For Hughes, the solution to the “too many eggs in too few baskets” conundrum was to build a force that could absorb significant but less-than-catastrophic losses while still retaining the firepower to hold the opponent’s fleet at risk.

In the nearly 15 years since Hughes raised the bimodal idea, the growth in the size of the People’s Liberation Army Navy (PLAN) and the expanding reach of its antiaccess and area-denial assets have given new urgency to developing a distributed offensive naval capability. Luckily for the U.S. Navy, new, inexpensive autonomous technologies offer a way to supplement its existing sea-control force that relies on the carrier strike group. A fleet of mostly small, inexpensive, and largely uncrewed offensive platforms could operate forward as sensors, decoys, and missile shooters, not only to absorb or misdirect the opponent’s first salvo, but also to engage the opponent’s sea-denial capabilities at the outset of a conflict. This bimodal approach to fleet design would allow the Navy to use its carrier strike groups as a sea-control force, protecting sea lines of communication from interdiction and harassment, while simultaneously using its sea-denial force to engage the PLAN’s growing offensive capability. A bimodal fleet allows the Navy to continue to operate its existing warships—built at enormous cost and operated with human capital that literally requires decades to develop—while creating cost-effective ways to deliver vast amounts of ordnance quickly and economically against a growing number of targets.

The economics and logic behind this sea-denial force are straightforward. For the cost of a single Arleigh Burke–class guided-missile destroyer (DDG), the Navy could purchase about 40 large autonomous surface vessels (LASVs) and equip each with eight cruise missiles or even more exotic air, surface, or subsurface long-range weapons. Instead of the missiles in a DDG’s approximately 90-plus vertical-launch cells, the new sea-denial force could bring nearly 320 missiles into a region, closing the gap in long-range offensive capability that exists between the PLAN and the U.S. Navy today.2 Jeffrey Kline has described how this sea-denial force might operate in practice:

Offensive antiship missiles are becoming smarter and our adversaries have learned to employ them in various ways: from shore, shipping containers, bombers and missile boats. Our own offensive fleet could be just as versatile, composed of missile corvettes paired with missile-equipped LASVs working in coordination with undersea systems and long-range bombers armed with hypersonic missiles. The objective of this force is to close silently and deceptively; deliver their missiles, torpedoes, mines or cyber packages; then retire, or, if unmanned, stay as a reconnaissance node, if desired.3

If remnants of the opponent’s surface fleet manage to escape the sea-denial force’s fires and head toward open waters, the Navy’s sea-control component could use its strike assets to engage them as they move toward our allies, forward bases, and sea lines of communication. The best news about the future bimodal U.S. Navy is that the sea-control force, the most expensive mode based around carrier strike groups, already exists. The cost of the new sea-denial force might not be insignificant, but it will only be a small fraction of the cost of the Navy’s existing ship-building plan.

The Bimodal Future

This bimodal future is beginning to manifest in several important ways. In May 2019, the Navy established its first surface development squadron, consisting of the USS Michael Monsoor (DDG-1001) and one Sea Hunter prototype medium displacement unmanned vehicle, with a second Sea Hunter arriving in fiscal year (FY) 2021. The Navy’s FY 2021 budget submission to Congress also focused on research and development funding to acquire several unmanned prototypes before shifting in F Y2023 to a procurement strategy that will accelerate in the out years. On 16 March 2021, the Navy released its strategy for developing, acquiring, and integrating various types of unmanned vehicles into the fleet. This strategy is just the latest in a series of initiatives to accelerate development and acquisition of a family of unmanned surface and subsurface vehicles.

Ronald O’Rourke of the Congressional Research Service notes that these developments reflect a growing recognition on the part of senior Navy officials that acquiring only manned, multimission, and expensive platforms will not answer the Navy’s need for a sea-denial force. Many senior officers seem to recognize the fact that unmanned systems are needed to complicate the opponent’s targeting problem by forcing it to detect, identify, and track scores if not hundreds of targets. Autonomous vessels would also enable new operational and tactical concepts because they could be deployed to areas too risky for manned ships, while loss of a handful of unmanned platforms would not constitute a significant decrease of overall naval capability.4

A cottage industry also has recently emerged that highlights novel deployment concepts for the sea-denial force. A group of observers led by T. X. Hammes, for instance, has suggested that the Navy might preposition repurposed merchant ships armed with missiles to bolster its sea denial capabilities in a pinch. Carrying a skeleton crew or even operating autonomously under certain conditions, these missile carriers could inexpensively deliver hundreds of weapons to the sea-denial fight. Robert Rubel has advanced a slightly more conventional idea: convert soon-to-be-retired Whidbey Island–class dock landing ships (LSDs) to “motherships” for a new type of autonomous antiship-missile craft, which would add a purpose-built and probably more survivable delivery mechanism to the sea-denial battle.

The key notion behind both schemes is to greatly increase the number of platforms that can undertake the sea-denial mission, while finding ways to limit the cost of carrying and distributing potentially thousands of missiles into a region. The sea-denial force is weapons-intensive, not platform-intensive. To keep it that way, Navy planners have to minimize the personnel and logistical costs associated with this new force. Planners will have to overcome the temptation to “gold-plate” systems that, by definition, have to be placed at risk. Adding defensive systems, crew quarters, and highly redundant mechanical and propulsion engineering to autonomous platforms adds cost without greatly contributing to offensive firepower. Planners and designers have to guard against capability and mission creep as they design new platforms whose greatest contribution might be found in their expendability.

Next Steps

While the operational and tactical benefits of a bimodal fleet are becoming increasingly apparent to planners, Navy officers have not yet tackled key operational issues that will emerge as the sea-denial capability matures. Congressional staffers have complained that they have not received analysis supporting the Navy’s movement toward a more distributed fleet architecture based on large unmanned vessels. They also have requested an explanation of how manned and unmanned systems will operate together in the future. Staffers also wonder about the relationship between the capabilities of new autonomous vessels and potential concepts of operation. In other words, will changes in operational concepts require significant adjustments in performance requirements on new unmanned vessels?5 Given the Navy’s track record of extensively exploiting analysis as a tool in assessing all sorts of procurement, personnel, logistical, and operational issues, the failure to begin the types of analysis requested by Congress might reflect a cultural reluctance to embrace sea-denial capabilities based on small ships, let alone autonomous vessels. The Navy has not identified or implemented the enterprise-wide changes that will have to take place to make the sea-denial segment of the bimodal Navy fully operational.

The strategic benefits of a bimodal fleet have attracted even less attention within the Navy than the analytical and operational issues identified by Congressional staffers. With the rise of great power competition, the Navy’s mission is slowly shifting from operations that were common during the past 30 years—power projection, forward presence, humanitarian operations—toward deterring the outbreak of war, specifically war at sea. Deterrence, especially conventional deterrence, is about to take center stage in naval strategy. While a robust warfighting capability plays a critical role in a deterrence strategy, deterrence might best be thought of as a peace-preservation strategy in that the primary goal of the future fleet will be to prevent the outbreak of war. Deterrence rests on a paradox: The more capable the Navy is to engage in a sea-denial campaign immediately at the start of hostilities, the less likely it will be to have to fight in the first place.

A distributed, robust sea-denial capability can bolster deterrence by reducing an opponent’s confidence that it can achieve its objectives and especially by eliminating the belief that it can obtain its objectives without much of a fight by presenting the United States with a fait accompli, thereby shifting the onus of escalation onto policymakers in Washington. This second idea actually is an enduring source of trouble in world politics because leaders rarely embark willingly on long, attritional campaigns to achieve their objectives. Instead, they tend to seek low-cost and quick ways to secure their goals and then bank on the expectation that their opponent will not be willing to pay the price in blood and treasure to return to the status quo ante bellum. For example, this was the calculation that led the Japanese to attack Pearl Harbor. The architects of this surprise attack did not believe they could defeat the United States in an extended war of attrition; nevertheless, they also did not believe that their American opponents would put up much of a fight either.

By packing a significant offensive punch at the outset of hostilities, a bimodal U.S. Navy might never be put to the test by even a modestly risk-averse opponent because it reduces optimism about the success of a “quick grab.” The ability to engage the opponent in a conventional battle at the outset of hostilities would undermine expectations of a quick and relatively painless victory. The fact that this new sea-denial force would pose an immediate and significant threat to the opponent’s surface, air, and subsurface forces would make it difficult to construct a convincing case that a quick grab can succeed. The sea-denial force would be too large, too distributed, and too powerful to be sidestepped or destroyed at the outset of hostilities. In other words, a bimodal Navy would be optimized for a U.S. deterrent strategy in the western Pacific because it would reduce incentives for the opponent to undertake a strategic surprise attack at the start of a war. It presents hundreds of targets for an attacker to engage, while decreasing the prospects of achieving a quick fait accompli by meeting any attack with significant countervailing force. The opportunity to create this kind deterrent effect is what makes a bimodal navy a strategic requirement for the United States.

Get to Work

The amount of work that has to be completed before the bimodal concept can be fully realized is significant. Early efforts have focused on the emerging technologies that will be incorporated into the new sea-denial force, not on the enterprise-wide changes that this effort will foster.6 Everything from educational offerings, to logistical systems, to basing, to doctrine and operations, and—most important—strategy, will have to be optimized so the sea-denial force can deter aggression.

Opposition to the emerging bimodal fleet has been muted, although concerns are often raised about any plan to field “autonomous” weapons. The Navy is in a good position to engage this criticism. It has developed a variety of command-and-control options for its new unmanned vessels: Human operators might be in the command loop; vessels might operate semiautonomously (i.e., with human operators monitoring decisions made autonomously by the vessels); unmanned vessels might be fully autonomous; or autonomous vessels might simply operate in conjunction with crewed warships.7 Indeed, the greatest threat to the new fleet architecture is an accumulating list of questions and unresolved operational and strategic issues. For example, how will these systems deploy? In allied ports? How will they be supported and maintained? Will they be able to communicate or develop emergent autonomous operations in a denied environments? There is only a limited amount of time to address these questions before the Navy’s experimentation with autonomous prototypes transitions to serial production of vessels.

Technologies are available to create a sea-denial fleet that can be the centerpiece of the U.S. maritime deterrence strategy in the western Pacific. The United States might be at a major inflection point in maritime history, a point at which new technologies are creating new opportunities to execute strategies that bolster U.S. national security in critical ways. Nevertheless, what happens next is largely in the hands of Navy sailors. They have to make enterprise changes and develop operational concepts to transform new technologies into the capabilities needed to make maritime deterrence a reality. The issues found at the nexus between the operational capabilities of the emergent sea-denial force and maritime deterrence also will keep future strategists and planners busy for decades to come.

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