war on the rocks

What DARPA’s Naval Drone Could Mean for the Balance of Power

July 9, 2015

Alongside all the furor of the last decade-and-a-half’s discussions of the operationally, legally, and morally transformative (or otherwise) consequences of unmanned and autonomous aerial vehicles — the now-ubiquitous “drones” debate — another area of remotely operated military technology has been steaming forward with much less fanfare: unmanned naval systems. Remotely operated submersibles are now integral parts of naval mine-hunting and submarine rescue. Other unmanned naval systems, such as Israel’s Protector unmanned surface vessel (USV) and in-development NATO equivalents, are more high-profile — and potentially more contentious — in their combination of armament and lack of onboard operators. Yet such USVs have thus far remained most relevant to low-level tactical challenges: close counter-terrorist protection of higher-value naval units (as with Protector), mine countermeasures, communications relay, rudimentary anti-submarine warfare (as with the U.S. Navy’s Fleet-class), and so forth.

Submarine-trailing “drones” approach realization

In among this array of essentially tactical innovations, however, lurks an experimental USV with the potential to have far-reaching strategic consequences right up to the nuclear level: the Anti-Submarine Warfare Continuous Trail Unmanned Vessel (ACTUV), under development by the U.S. Defense Advanced Research Projects Agency (DARPA). The rationale for ACTUV is that by achieving and then autonomously maintaining a surface trail on the submarines of adversaries, the U.S. Navy will be well placed to overcome the threat potentially posed by such submarines — quiet diesel-electric submarines (SSKs, in naval hull classification parlance), in particular — to its freedom of maritime maneuver, especially the operations of carrier strike groups.

If it can be made to work, ACTUV — and eventual non-American ACTUV rivals — may have profound implications for both the naval and nuclear strategic balances. Of course, “if it can be made to work” is a substantial proviso. Tracking a submarine from a surface ship — or from another submarine, for that matter — is a challenging undertaking even in benign conditions, given the minimal acoustic signature of the best SSKs. A competent submarine commander can also maximize his relative advantage by using the thermocline, changes in speed/depth/heading, bathymetric features, the hunting ship’s own acoustic profile and other limitations/vulnerabilities, decoys, surface or environmental disturbance, and so forth, to full effect. The conditions in which ACTUV would be operating, moreover, may in fact be far from benign: If ACTUV can indeed be made operational, it seems likely that one or more unfortunate “accidents” between the U.S. Navy vessel — which, being unmanned, would find it hard to prove otherwise — and robustly built “fishing” boats could become a standard part of Chinese, Russian, or Iranian peacetime delousing practice for one of their boats going on patrol. If it was not peacetime, moreover, the ACTUV might be subject to an even more forceful response.

To be sure, a fully effective and reliable ACTUV system is likely to be decades rather than merely years away. Nonetheless, let us posit here that ACTUV can be made to work and that potential adversaries’ delousing procedures can be overcome; DARPA employs some very smart people, after all. The current surface version of ACTUV, moreover, could itself be a mere developmental precursor to an eventual submersible ACTUV, which would then pose a much more serious delousing challenge for opponents (as well as the mother of all collision-avoidance challenges in the vicinity of fishing fleets). Thus, hypothesizing that it can be made effective, the key to understanding the strategic consequences of both the United States’ ACTUV — and U.S. rivals’ comparable future developments — over both the short and long term then becomes an assessment of different states’ relative dependence on submarines for the accomplishment of key military tasks.

Short-term conventional benefits, long-term nuclear questions?

In the short term, an operationally effective ACTUV capability would confer a welcome strategic advantage on the United States and its major allies. SSKs represent one of the most popular and potentially capable means of attempting to generate sea denial against the U.S. Navy’s otherwise overwhelming preponderance (p. 194): Well-handled opposing submarines, particularly quiet diesel-electric boats, are the stuff of nightmares for Western surface task group commanders. Friendly nuclear-powered hunter-killer submarines (SSNs) can attempt to trail such boats out of port, of course, but SSNs are expensive and manned — and thus scarce and dangerous-to-risk — assets. If NATO naval intelligence had a constant grip on the locations of adversaries’ boats, by contrast, courtesy of ACTUV trails, then one of the principal obstacles to deploying high-value units into potentially hostile waters would be much reduced. To the extent that the rise of hostile anti-access/area denial (A2/AD) capabilities — particularly in the context of the East Asian littoral — are a pressing concern of U.S. strategists, therefore, the ability to keep tabs on rivals’ SSKs would provide one less headache when required to operate major surface platforms in such theatres. Of course, other emerging A2/AD headaches — such as anti-ship cruise/ballistic missiles and anti-satellite weaponry — are likely to endure and intensify, regardless of ACTUV; but even fighting a pitched anti-air battle is simplified significantly by the absence of a pressing underwater threat.

In the initial ACTUV age, therefore, the ability to keep track of rivals’ potentially hostile submarines looks like an unambiguous win for the United States and its allies. In the longer term, however, the diffusion of ACTUV-like technology — which we can assume U.S. rivals would pursue, especially if the U.S. version had been shown to deliver military advantages — may produce less welcome strategic consequences for Western powers. Again, this assessment is based on an appraisal of relative submarine dependence. In pursuing SSK-based sea denial capabilities against U.S. and allied naval preponderance, the balance of relative submarine dependence lies with America’s potential opponents. But in an even more critical domain of strategy — nuclear posture — the balance of relative submarine dependence actually lies with the West.

NATO’s three nuclear powers rely more heavily on submarines for the survivable delivery of their weapons than their principal potential adversaries. Britain’s nuclear arsenal is wholly submarine-based, and set to remain so. France’s arsenal is also predominantly based on ballistic missile submarines (SSBNs), barring a handful of remaining air-launched sub-strategic weapons. Even the mighty United States — long confident of the undetectability of its submarines — relies on SSBNs to provide the survivable component of its nuclear triad: Air Force strategic bombers are no longer kept permanently airborne with nuclear payloads, and the ground-based arsenal lacks a road- or rail-mobile component. By contrast, while China and Russia both operate SSBNs — the latter much more successfully than the former, thus far — neither trusts so completely in their submarine-based arsenals as their Western counterparts, precisely because of an enduring lack of confidence in their SSBNs’ ability to avoid Western detection. Instead, they have pursued hardened tunnel systems and road-mobile launchers as a way of bolstering the survivability of their nuclear forces. While such land-based hardening may have delivered only questionable success, it undeniably makes for more non-submarine-based nuclear survivability than no non-submarine-based survivability at all. If non-NATO ACTUV systems — or some other variant of SSBN-following “drone” — become operationally effective at some point following the initial U.S. development of the technology, therefore, this could have significant consequences for the survivability of Western nuclear arsenals. Such consequences would in turn carry implications for strategic stability and the balance of power.

Let’s not get too excited…

None of this is to say that DARPA should not press ahead with its development of ACTUV. Since Russia and China are likely to seek to develop their own similar systems anyway, the United States and its allies may as well benefit from a passing window of relative advantage. Similarly, this is not to say that Western SSBNs are suddenly about to become “easy” to trail: Major NATO powers have displayed a continuing ability to “blow away” even their closest and most capable allies with their advances in submarine warfare, and with both the U.S. and Royal Navies currently developing new SSBN classes, both nations’ missile boats look set to remain at the technological cutting edge for the foreseeable future. Certainly, given the risks and dangers associated with land basing of strategic nuclear weapons — namely, the vulnerability of silos and similar facilities to first strikes — SSBNs will be by far the most desirable delivery system as long as non-Western ACTUV-like systems are anything other than capable and numerous. Even if the likes of China and Russia do subsequently develop ACTUV-like systems of their own, moreover, this is not to say that they will be anywhere near as good as the U.S. version(s) anytime soon, if ever, or that Western boats will not be able to readily evade them through their own delousing protocols. And of course, it could be that such an experimental system as ACTUV eventually proves unworkable at the operational level, meaning that neither the benefits nor the drawbacks discussed here ever come to fruition.

Nevertheless, the rise of the submarine-trailing naval drone — of which DARPA’s ACTUV is the first concrete example of a previously mooted concept — could yet have substantial strategic consequences at both the conventional and nuclear levels. On the former, ACTUV could provide a limited reversal of rivals’ A2/AD capabilities, and thus a partial restoration of Western navies’ freedom of maritime maneuver. Yet on the latter, while SSBNs remain by far the most secure nuclear delivery system for the present and immediate future, the day when NATO’s nuclear powers have to contemplate augmenting them with other approaches to developing nuclear survivability may just about be creeping onto the horizon.


David Blagden is a Lecturer in International Security and Strategy at the University of Exeter. He is also an officer in the Royal Naval Reserve, but stresses that this is work completed in his civilian academic capacity; it does not reflect the official views of — and has not received input from — the Royal Navy or the U.K. Ministry of Defence. He tweets @blagden_david.


Photo credit: Official U.S. Navy Imagery