Lockheed Martin
A lack of defensive options against swarms of UAVs imperils the fleet.
On board the USS George H. W. Bush (CVN-77) in the summer of 2014, I was the executive officer of Helicopter Maritime Strike Squadron 70 as we steamed through the Strait of Hormuz. I stood amazed as an Iranian drone* circled lazily overhead. Decidedly low-tech, the unmanned aerial vehicle had managed to get into the heavily monitored and controlled airspace above the aircraft carrier and its air defense escort ships.
Little did I know then that the slow, small aircraft represented new risks to U.S. naval forces and would demand a shift in mind-set. Drone technology has advanced quickly since. Iranian Predator-like drones have conducted numerous precision strikes in Syria. In the near future, these armed unmanned systems likely will circle over a U.S. aircraft carrier as it transits the Strait of Hormuz or the Bab el-Mandeb. Swarms of such drones soon could challenge maritime freedom of navigation and the safe operations of the U.S. Navy and our allies nearly anywhere in the world.
Rapid advancement and transfer of drone technology have transformed land warfare, and drones will soon transcend their traditional surveillance role in the maritime domain as well. Until recently, the technology required for long-range drone control has hindered their maritime employment by nations without the necessary infrastructure. The latest innovations, however, are making such investment moot.
Precision-strike, non-line-of-sight (NLOS) control, and swarming technologies formerly reserved for the world’s large military powers are trickling down to provide asymmetric capabilities for weaker states and non-state actors. Correspondingly, defense against maritime drones is complicated because of the constraints of international law, the difficulty in determining hostile intent, and an inefficient kill chain or means of response. To meet the advancing unmanned threat, policy changes and technological investment are necessary to preserve a ship captain’s decision-making space throughout the “find, fix, finish” kill chain.
Armed Drones in the Maritime Domain
In Syria, armed Iranian Shahed-129 drones have executed precision air-to-surface strikes, despite a lack of satellite-navigation-enabled targeting or control links. This is a capability the United States and then Israel took decades and billions of dollars to acquire. In Japan, mobile phone signals were used to control a drone at a range of 50 kilometers, extending the line-of-sight command-and-control link. Whether Iran builds additional cell towers along the country’s coast, develops a drone-based communication relay capability, or consummates a proposed Chinese technology-transfer and satellite deal, Iranian forces likely will leverage new technology soon to provide U.S. Predator-like strike capability in the Gulf of Oman and the Arabian Gulf.
Consequently, the airspace above two strategic geographic choke points—the Bab el-Mandeb and the Strait of Hormuz—could, within a few years, be teeming with armed drones. Over the past three decades, Iran has built a robust drone-support infrastructure, adding or improving at least four drone bases both in and outside the Arabian Gulf. Extended runways, mobile radar monitoring stations, and hangars allow Iran to engage in reconnaissance over large swaths of the Arabian Gulf and the Gulf of Oman and have led to increased interactions with U.S. ships. Iran’s alleged development of kamikaze drones and successful use of armed attack drones, coupled with the Islamic Revolutionary Guard Corps Navy’s (IRGCN’s) penchant for operating in an “abnormal and unprofessional” manner, intensify risk in the strait.1
Air Defense in a Drone-Infested Environment
Unmanned systems complicate air defense and have proven a significant problem for “find, fix, and finish” kill chains. While simply destroying all threatening unmanned systems would seem to be an easy answer for ship defense, such logic could facilitate another tragedy like the 1988 USS Vincennes (CG-49) incident. In that case, a U.S. ship, while locked in a surface engagement with small boats, believed it also was under air attack and mistakenly destroyed an airliner. U.S. Navy tactical advancements that have reduced the risk of another such incident would be wasted by engaging all unmanned air vehicles that appear threatening. Moreover, the United States considers unmanned systems to be “sovereign immune vessels,”2 and such aggressive action would open our drones to casual destruction. It is therefore imperative that defensive gaps exploited by unmanned systems be filled in a manner that respects their responsible use.
Air defense operators are assigned to track air contacts in the often-busy airspace over the Arabian Gulf. Applying dozens of assessment factors, they build profiles for each radar track to determine whether a given aircraft threatens their ship. Speed, altitude, flight profile, country of origin, identification friend or foe (IFF) signal, and many other inputs are filtered through the real-time geopolitical threat context to build the air picture surrounding a ship. Some ships, like Aegis cruisers and destroyers, are built for air defense and have advanced radar and command and weapons control computers that facilitate such complex decisions. Many ships, including aircraft carriers, do not. In all cases, air defense operators with sufficient time will conduct preplanned responses (PPR)—actions designed to force a threatening aircraft to declare its intentions. The process is tuned to maximize decision-making time and to keep the threat well outside the minimum ranges of a ship’s defensive systems. Drones complicate this process because they are hard to find, hard to track, and can be surprisingly hard to kill.
Finding a drone is critical to mitigating its threat. Even the world’s most advanced radar systems have problems with low, slow, small objects. A low-flying drone’s small radar signature is difficult to pick out of sea clutter, reducing recognition and reaction time. Smaller drones, including the ubiquitous quadcopter, typically are made of plastic, further reducing their radar signature. These drones can be launched from small boats near a warship, significantly compressing reaction and decision-making time. Moreover, a quadcopter’s ability to hover for an extended period lowers its Doppler signature, evading most Doppler-tracking maritime radar systems. While systems like the AN/SPY-1, the powerful phased-array radar that is part of the Aegis tactical system, can track very small targets at ranges in excess of 100 kilometers, distortion of radar energy near the water’s surface or near land can allow for what are known as sanctuaries. U.S. ships not equipped with phased-array radar systems are at a significant disadvantage when trying to pick out a threatening quadcopter in the sea clutter.
Once detected, aircraft approaching U.S. naval forces are “fixed” in space, meaning they are tracked and identified. Drones are harder than manned aircraft to manage in this phase, and radar systems that cannot easily find drones also strain to track them. Quadcopters and other battery-operated systems do not provide a large enough infrared signature for long-range tracking. Too fast for helicopters yet too slow for fighters to escort efficiently, drones inhabit a gray zone where they are identified, tracked, and monitored electronically but not continuously escorted. Large numbers of drones quickly would overwhelm any manned-aircraft capability to intercept them while also overwhelming the shipboard watch operators tasked with maintaining, sorting, and mitigating them.
To “finish” or destroy a drone, a ship’s commander must declare it hostile. Here, freedom of overflight enshrined in international law and differences in determining the hostile intent of unmanned versus manned systems make self-defense difficult.
Policy Options to Face the Approaching Swarm
Policy changes in drone airspace use and ship air defense, facilitated by new technology to aid detection and accelerate defensive decision making, are needed to provide U.S. Navy commanders the tools to keep their ships safe and prevent the first counter-drone incident from setting an inappropriate precedent.
Such a policy change should be informed by the existing Federal Aviation Administration (FAA) and International Civil Aviation Organization (ICAO) effort to introduce unmanned aircraft into the civil aviation airspace. Despite their many variations, unmanned air vehicles (UAVs) are being classed into two categories: those that can join the civil airway system and those too small or underdeveloped to do so. Though military drones, like all state aircraft (e.g., those used in military, customs, and police services), are exempt from ICAO governance, this distinction could help inform resolution of the stickier problem of determining unmanned system sovereignty.
Regulations will be critical as nations begin to determine what and how UAVs can be used. A drone that can broadcast its position, react and respond to air traffic control instructions, is certified for flight over populated areas, and can sense and avoid other air traffic would be considered a smaller risk to naval forces. Small drones without these capabilities give no information about their capability and provide no method to deduce their intent, increasing the risk posed to a ship.
In the context of international airspace, changes to UAV use should be driven through ICAO regulation updates, education on domestic drone use, and the temporary reserving of airspace for safe ship passage. To transform UAV use durably enough to create international norms, existing regulatory documents need to be revised. The U.S. military can accelerate this process by updating Standards and Recommended Practices and Procedures for Air Navigation Services. Desired behavioral norms should be regulated, promulgated, and enforced first within the United States. To set a precedent for expanded restrictions outside U.S. territorial airspace, laws should initially be developed that restrict UAV flight over Navy warships in port or within U.S. territorial waters. The changes should be disseminated via public education campaigns. Subsequently, UAV restrictions would become normal, much as boat-traffic restrictions around U.S. warships following the al Qaeda attack on the USS Cole (DDG-67) in October 2000 have become routine worldwide.
The United States also should use existing systems to establish airspace restrictions on UAV use over U.S. warships immediately, while policy changes are incorporated in the respective bureaucracies. The best tool for implementing such an airspace restriction is the Notices to Airmen (NOTAM) reporting system. Through creative use and careful screening, NOTAMs could give U.S. warships breathing space when they sail through high-risk waterways, without compromising operational security.
Though U.S. warships are fastidious about proper identification and use of PPRs, UAVs obfuscate an already complex air picture in the Arabian Gulf. For ships outfitted with SPY-1 radar, dwell times and speed gates must be adjusted in combat system standard operating procedures to allow for better identification of low, slow, small aircraft. Ships that lack high-end radar systems can be supported by those that have them, or supplemented through bolt-on systems designed to find UAVs. Just as small-boat interactions are tracked closely by U.S. Naval Forces Central Command, UAV interactions must be tracked and reported in a standardized manner to establish patterns and inform future decisions on the use of force. Unprofessional, unsafe UAVs that ignore NOTAM air restrictions, do not signal their positions, do not respond to warnings, and thus put a warship at risk should be disabled, destroyed, or captured.
To meet the rising UAV threat, U.S. Defense Department funding for technology is needed. Already, counter-UAV technology is rapidly advancing, fueled by a deluge of commercial investment expected to exceed $1.1 billion by 2022.3 Black Dart, the Navy’s annual counter-drone exercise, tested nine counter-UAV systems successfully in 2015. Even so, little emphasis was placed on developing technology to determine hostile intent, the crucial decision required before counter-UAV weapons can be used. While current policy forces UAVs to operate in a manner that fits existing query-warn-kill PPRs, money must be invested in technology that provides warships with methods to warn before engagement. Systems like the Blighter Anti-UAV Defense System optical disruptor, which attacks the UAV camera’s automatic gain system to temporarily blind the drone, or laser systems that can temporarily blind the UAV’s optical sensor to alert the remote pilot to danger, are worth pursuing but have limited practically. An approaching non-squawking, non-communicating aircraft will always be assumed to be manned; therefore, most of these systems will not be used until the UAV is positively identified.
International counter-drone policy is undefined, but a precedent is forming that tends toward permitting defensive measures. In 2015, China attempted to jam a U.S. Global Hawk as it flew over international waters, ostensibly to push it away from the South China Sea. In 2016, in the same area, China captured a U.S. submersible drone. In both cases, such action likely would have had more severe ramifications if taken against manned systems. In any domain, dissuasion or drone destruction has yet to be construed as a casus belli. Israeli forces have routinely shot down drones in their airspace, including one attempt against a Russian drone,4 without conflict escalation. In yet another example, Japan, after regularly experiencing airspace incursions by the Chinese, issued rules of engagement that authorize destruction of UAVs that fail to heed warnings. Such actions are more likely to lead to a maritime claim for property loss in an admiralty court than war.
Technology Facilitates Present Defense and Future Domination
Even with an improved ability to find and track UAVs and better policy and methods to determine hostile intent, gaps remain in the U.S. ability to mitigate the threat — namely, drones are difficult to destroy. While U.S. ships can handle antiship cruise missiles (ASCMs), as shown recently in the Red Sea, recent counter-drone operations in Israel demonstrate that kinetic defenses may not always work against unmanned vehicles. Drone swarms pose a bigger problem. A 2012 Naval Postgraduate School study found through a series of simulations that four of eight kamikaze drones would frequently penetrate an Arleigh Burke–class destroyer’s defenses.5 A UAV swarm in greater numbers would rapidly overwhelm a ship.
To fortify U.S. counter-drone defenses, priority of effort should be given to improving U.S. fleet point defenses to mitigate the immediate threat, with priority funding for measures to determine hostile intent and facilitate swarm defense. Immediate areas of focus could include electronic warfare, kinetic point-defense systems, and directed-energy weapons.
Electronic warfare suites, designed to defend against ASCMs by jamming their control signals, would likely need to be tuned to the proper power and spectrum to disrupt a drone, possibly leaving the ship open to ASCM attack. Severing the control link through electronic attack may be the one way to immediately neutralize a swarm.6
Point-defense systems, for their part, provide adequate self-defense for the near term but will not be sufficient to meet multiple swarming UAVs. The Phalanx close-in weapon system (CIWS), firing more than 4,500 bullets per minute, is the best anti-drone system in the fleet but can engage for only twenty seconds at a time, spread among incoming targets. To improve CIWS counter-drone effectiveness, necessary upgrades include increasing the magazine size, decreasing the cycle time (time between engagements), and reducing ammunition required per engagement.
Directed-energy weapons, either microwave weapons or lasers, show the greatest promise for drone defense. With an instantaneous ability to strike and nearly inexhaustible “ammunition,” this option is limited only by weather, range, and cycle time. But more powerful systems than are currently available are required to increase effective range and reduce the energy and time necessary to destroy each target. Moreover, Protocol IV of the 1980 Convention on Certain Conventional Weapons, the “Protocol on Blinding Laser Weapons,” complicates matters for light-sourced systems. Until ships can confidently determine whether an incoming aircraft is manned or unmanned, laser weapons will not find heavy use against air targets.
Drones themselves, with air-intercept capability, may be the future of fleet drone defense. The Naval Postgraduate School and Office of Naval Research’s Project LOCUST7 (Low-Cost UAV Swarming Technology) has flown swarms of more than 30 aircraft with test plans for a 50-on-50 UAV semiautonomous battle scheduled within the next year. LOCUST has a launch system that can put 30 drones airborne in just over 30 seconds and a control system that can fly them in a swarm. Currently, drones heading toward an aircraft carrier prompt a launch of the ready “alert” fighters for intercept and escort. Regardless of the type of drone, an F/A-18 and a fuel tanker are catapulted off the aircraft carrier and end up escorting the typically slow UAV by flying tight circles around it. Besides reducing the number of alert aircraft ready to respond to other threats, the aircraft waste upward of $25,000 in fuel responding to a drone approach. At approximately $15,000 a piece, LOCUST could launch drones from a helicopter or any ship in the U.S. inventory, which could then intercept, identify, escort, and disable an incoming drone. The visual identification and verification of the unmanned aircraft would also allow the ship to use directed energy weapons in point defense if the drone couldn’t destroy the incoming UAV.
Conclusion
Unmanned vehicles have changed warfare, and drone swarms are rapidly becoming a reality. China recently flew 67 drones in a semiautonomous swarm demonstration, the largest in history, and Iranian drones are growing increasingly capable. Current U.S. combat systems can handle a drone or two, but not a swarm. In a training accident in November 2013, a U.S. target drone crashed into the cruiser USS Chancellorsville (CG-62) causing $30 million in damage and a six-month layup for repairs.8 A malfunctioning drone flying a thousand feet over an aircraft carrier could descend in under 30 seconds and damage the flight deck, a radar panel, or expensive combat aircraft parked on deck. A swarm of drones intentionally flown into the ship could wreak even greater damage.
Better international and U.S. Navy policy, improved awareness of the battlespace, electronic attack systems that can nullify a swarm, and directed-energy systems to destroy drones that get through will help U.S. ships survive an enemy drone attack. Furthermore, defensive counter-air drone swarms, launched and controlled by ships, aircraft, and submarines miles ahead of a strike group, could effectively counter this threat at beyond-visual range and help U.S. ships accomplish their broader missions in a drone-saturated environment.
*The term “drone” for the purposes of this article refers to an unmanned aerial vehicle, or UAV, and is used interchangeably.
1. Galen Wright, “Examining Drone Strikes in Syria,” Offiziere.ch, 29 February 2016, http://offiziere.ch/?p=26604.
2. Peter Cook, “Statement by Pentagon Press Secretary Peter Cook on Return of U.S. Navy UUV,” U.S. Department of Defense, 19 December 2016, www.defense.gov/News/News-Releases/News-Release-View/Article/1034224/statement-by-pentagon-press-secretary-peter-cook-on-return-of-us-navy-uuv.
3. Giulia Tilenni, “Counter UAV: Defeating the Device,” Defense Procurement International, 14 September 2016, www.defenceprocurementinternational.com/features/air/counter-uav-devices-feature-air.
4. Michael Peck, “Israel Almost Shot Down a Russian Drone,” The National Interest, 16 August 2016, http://nationalinterest.org/feature/israel-almost-shot-down-russian-drone-17390.
5. Demonstenes Balbuena, Michael Casserly, Brandon Dickerson, Stephen Graves, Vincente Maldonado, Bhavisha Pandya, Loc Pham, James Sanders, “UAV Swarm Attack: Protection System Alternatives for Destroyers,” Naval Post Graduate School, December 2012, http://calhoun.nps.edu/handle/10945/28669.
6. Ibid.
7. Patrick Tucker, “The Navy is Preparing to Launch Swarm Bots Out of Cannons,” Defense One, 14 April 2014, www.defenseone.com/technology/2015/04/navy-preparing-launch-swarm-bots-out-cannons/110167/.
8. “Navy: Six Months of Repairs to Drone-Struck Ship Will Cost $30 Million,” USNI News, 30 December 2013, https://news.usni.org/2013/12/30/navy-six-months-repairs-drone-struck-ship-will-cost-30-million.