Category Archives: Drones

Operating in an Era of Persistent Unmanned Aerial Surveillance

By William Selby

In the year 2000, the United States military used Unmanned Aerial Systems (UASs) strictly for surveillance purposes and the global commercial UAS market was nascent. Today, the combination of countries exporting complex UAS technologies and an expanding commercial UAS market advances the spread of UAS technologies outside of U.S. government control. The propagation of this technology from both the commercial and military sectors will increase the risk of sophisticated UASs becoming available to any individual or group, regardless of their intent or financial resources. Current and future adversaries, including non-state actors, are likely to acquire and integrate UASs into their operations against U.S. forces. However, U.S. forces can reduce the advantages of abundant UAS capability by limiting the massing of resources and by conducting distributed operations with smaller maneuver elements.

Leveraging the Growth in the Commercial UAS Market

While armed UAS operations are only associated with the U.S., UK, and Israel, other countries with less restrictive export controls are independently developing their own armed UAS systems. Chinese companies continue to develop reconnaissance and armed UASs for export to emerging foreign markets. Earlier this year, social media reports identified a Chinese CH-3 after it crashed in Nigeria. Reports indicate China sold the system to the Nigerian government for use against Boko Haram. Other countries including Pakistan and Iran organically developed armed UAS capabilities, with claims of varying levels of credibility. In an effort to capitalize on the international UAS market and to build relationships with allies, the U.S. eased UAS export restrictions in early 2015 while announcing the sale of armed UASs to the Netherlands. Military UAS development is expected to be relatively limited, with less than 0.5 percent of expected future global defense spending slated to buying or developing military drones. For now, long range surveillance and attack UASs are likely to remain restricted to the few wealthy and technologically advanced countries that can afford the research costs, training, and logistical support associated with such systems. However, short range military or civilian UASs are likely to be acquired by non-state actors primarily for surveillance purposes.

Still captured from an ISIS documentary with footage shot from a UAS over the Iraqi city of Fallujah(nytimes.com)

Still captured from an ISIS documentary with footage shot from a UAS over the Iraqi city of Fallujah(nytimes.com)

Hamas, Hezbollah, Libyan militants, and ISIS are reportedly using commercial UASs to provide surveillance support for their military operations. Current models contain onboard GPS receivers for autonomous navigation and a video transmission or recording system that allows the operators to collect live video for a few thousand dollars or less. Small UASs, similar in size to the U.S. military’s Group 1 UASs, appeal to non-state actors for several reasons. Namely, they are inexpensive to acquire, can be easily purchased in the civilian market, and are simple to maintain. Some systems can be operated with very little assembly or training, which reduces the need for substantial technical knowledge and enables non-state actors to immediately integrate them into daily operations. These UASs are capable of targeting restricted areas as evidenced by the recent UAS activity near the White House, French nuclear power plants, and the Japanese Prime Minister’s roof. The small size and agility of these UASs allow them to evade traditional air defense systems yet specific counter UAS systems are beginning to show progress beyond the prototype phase.

Economic forecasters may dispute commercial UAS sales predictions, but most agree that this market is likely to see larger growth than the military market. Countries are currently attempting to attract emerging UAS businesses by developing UAS regulations that will integrate commercial UASs into their national airspace. The increase of hobby and commercial UAS use is likely to lead to significant investments in both hardware and software for these systems. Ultimately, this will result in a wider number of platforms with an increased number of capabilities available for purchase at a lower cost. Future systems are expected to come with obstacle avoidance systems, a wider variety of modular payloads, and extensive training support systems provided by a growing user community. Hybrid systems will address the payload, range, and endurance limitations of the current platforms by combining aspects of rotor and fixed wing aerial vehicles. The dual-use nature of these commercial systems will continue to be an issue. Google and Amazon are researching package delivery systems that can potentially be repurposed to carry hazardous materials. Thermal, infrared, and multispectral cameras used for precision agriculture can also provide non-state actors night-time surveillance and the ability to peer through limited camouflage. However, non-state actors will likely primarily use hobby and commercial grade platforms in an aerial surveillance role, since current payload limitations prevent the platforms from carrying a significant amount of hazardous material. 

Minimizing the Advantages of Non-State Actor’s UAS Surveillance

As these systems proliferate, even the most resource-limited adversaries are expected to have access to an aerial surveillance platform. Therefore, friendly operations must adapt in an environment of perceived ubiquitous surveillance. Despite the limited range and endurance of these small UASs, they are difficult to detect and track reliably. Therefore, one must assume the adversary is operating these systems if reporting indicates they possess them. Force protection measures and tactical level concepts of operations can be modified to limit the advantages of ever-present and multi-dimensional surveillance by the adversary. At the tactical level, utilizing smoke and terrain to mask movement and the use of camouflage nets or vegetation for concealment can be effective countermeasures. The principles of deception, stealth, and ambiguity will take on increasing importance as achieving any element of surprise will become far more difficult. 

The upcoming 3DR Solo UAS will feature autonomous flight and camera control with real time video streaming for $1,000 (3drobotics.com)
The upcoming 3DR Solo UAS will feature autonomous flight and camera control with real time video streaming for $1,000 (3drobotics.com)

At static locations such as forward operating bases or patrol bases, a high frequency of operations, including deception operations, can saturate the adversary’s intelligence collection and processing capabilities and disguise the intent of friendly movements. Additionally, massing strategic resources at static locations will incur increasing risk. In 2007 for example, insurgents used Google Earth imagery of British bases in Basra to improve the accuracy of mortar fire. The adversary will now have near real time geo-referenced video available which can be combined with GPS guided rockets, artillery, mortars and missiles to conduct rapid and accurate attacks. These attacks can be conducted with limited planning and resources, yet produce results similar to the 2012 attack at Camp Bastion which caused over $100 million in damages and resulted in the combat ineffectiveness of the AV-8B squadron.

In environments without the need for an enduring ground presence, distributed operations with smaller maneuver elements will reduce the chance of strategic losses while concurrently making it harder for the adversary to identify and track friendly forces. Interestingly, operational concepts developed by several of the services to assure access in the face of sophisticated anti-access/area denial threats can also minimalize the impact of the UAS surveillance capabilities of non-state actors. The Navy has the Distributed Lethality concept, the Air Force is testing the Rapid Raptor concept, and the Army’s is developing its Pacific Pathways concept. The Marine Corps is implementing its response, Expeditionary Force 21 (EF21), through several Special Purpose Marine Air Ground Task Forces.

The EF21 concept focuses on using high-speed aerial transport, such as the MV-22, to conduct dispersed operations with Company Landing Teams that are self-sufficient for up to a week.  In December 2013, 160 Marines flew over 3,400 miles in KC-130s and MV-22s from their base in Spain to Uganda in order to support the embassy evacuation in South Sudan, demonstrating the EF21 concept. Utilizing high speed and long-range transport allows friendly forces to stage outside of the adversary’s ground and aerial surveillance range. This prevents the adversary from observing any patterns that could allude to the mission of the friendly force and also limits exposure to UAS surveillance. Advances in digital communications, including VTCs and mesh-networks, can reduce the footprint of the command center making these smaller forces more flexible without reducing capabilities. The small size of these units also reduces their observable signatures and limits the ability of the adversary to target massed forces and resources.

Confronting the Approaching UAS Free-Rider Dilemma

Non-state actors capitalize on the ability to rapidly acquire and implement sophisticated technologies without having to invest directly in their development. These organizations did not pay to develop the Internet or reconnaissance satellites, yet they have Internet access to high-resolution images of the entire globe. It took years for the U.S. to develop the ability to live stream video from the Predator UAS but now anyone can purchase a hobby UAS that comes with the ability to live stream HD video to YouTube for immediate world-wide distribution. As the commercial market expands, so will the capabilities of these small UAS systems, democratizing UAS technology. Systems that cannot easily be imported, such as advanced communications relays, robust training pipelines, and sophisticated logistics infrastructure can now be automated and outsourced. This process will erode the air dominance that the U.S. enjoyed since WWII, now that commercial investments allow near peers to acquire key UAS technologies that approach U.S. UAS capabilities.

The next generation of advanced fighters may be the sophisticated unmanned vehicles envisioned by Navy Secretary Ray Maybus. However, other countries could choose a different route by sacrificing survivability for cheaper, smaller, and smarter UAS swarms that will directly benefit from commercial UAS investments. Regardless of the strategic direction military UASs take, commercial and hobby systems operating in an aerial surveillance role will remain an inexpensive force multiplier for non-state actors. Fortunately, the strategic concepts developed and implemented by the services to counter the proliferation of advanced anti-air and coastal defense systems can be leveraged to minimalize the impact of unmanned aerial surveillance by the adversary. Distributed operations limit the massing of resources vulnerable to UAS assisted targeting while long-range insertions of small maneuver elements reduces the exposure of friendly forces to UAS surveillance. Nation states and non-state actors will continue to benefit from technological advances without investing resources in their development, pushing U.S. forces to continually update operational concepts to limit the increasing capabilities of the adversary.

William Selby is a Marine officer who completed studies at the US Naval Academy and MIT researching robotics and unmanned systems. He previously served with 2nd Battalion, 9th Marines and is currently stationed in Washington, DC. Follow him @wilselby or www.wilselby.com 

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Inspector Gadgets: Drones in the Hangar

Checking an aircraft for damage can be arduous and meticulous work,  but last week’s issue of The Economist highlights an experimental commercial approach. In simple terms, the Remote Intelligent Survey Equipment for Radiation (RISER) drone is a quadcopter with LIDAR and forms the basis for a system to use lasers to automatically detect damage to airliners.

The obvious naval application for inspector drones would be for ground-, carrier, and surface vessel-based fixed-wing and helicopter units, although the configurations for each aircraft type and location might make some more practical than others. For example it probably makes more sense to consolidate expertise in inspector drones at regional maintenance and readiness centers than to try to outfit a unit in the small helicopter hangar of every destroyer. But there’s always something to be said for an operational capability.

While The Economist notes that the drones are allowed at Luton airport, UK, to “operate only inside hangars, and only when the doors are shut,” similar systems could be used during periods of extended surface ship and submarine maintenance, particularly while in dry dock to check for damage and wear and tear to those vessels’ hulls and systems.

We’ve speculated previously at CIMSEC on the utility of LIDAR-equipped shipboard robots and autonomous systems to engage in damage control, but external hull and airframe inspection drones add a wrinkle and join an ever-growing list of potential (and actualized) uses for drones.

Scott Cheney-Peters is a surface warfare officer in the U.S. Navy Reserve and founder and Chairman of the Center for International Maritime Security (CIMSEC). He is a graduate of Georgetown University and the U.S. Naval War College, a member of the Truman National Security Project, and a CNAS Next-Generation National Security Fellow.

CIMSEC content is and always will be free; consider a voluntary monthly donation to offset our operational costs. As always, it is your support and patronage that have allowed us to build this community – and we are incredibly grateful.

A Survey of Missions for Unmanned Undersea Vehicles: Publication Review

As a closer to last week’s run of UUV articles – a publication review by Sally DeBoer, UUV week’s associate editor.

 

Screen Shot 2015-05-25 at 5.02.27 PM

Discussion of how the world’s navies will incorporate unmanned underwater vehicles into their doctrine and infrastructure is very broad indeed. Will these technologies be complementary to existing architecture or stand-alone platforms? Will they operate autonomously (indeed, can we even achieve the degree of autonomy required?) or with a man-in-the-loop? Perhaps because the technology is so (relatively) new and (relatively) unestablished, with potential applications so vast, the conversation surrounding it blurs the line between what is and what if.

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Conceptualization of the US Navy UUV concept

Thankfully, the meticulous staff at the RAND Corporation’s National Defense Research Institute, sponsored by the US Navy, produced a thorough and carefully researched study in 2009 outlining the most practical and cost-effective applications for underwater technologies. Using the US Navy’s publically-available 2004 UUV Master Plan (an updated version of this document was produced in 2011 but has not been released to the public) as a jumping off point, the authors of the study evaluated the missions advocated for UUVs in terms of military need, technical risks (as practicable), operational risks, cost, and possible alternatives. Analyzing an “unwieldy” set of 40 distinct missions spanning nine categories initially advocated in the 2004 version UUV Master Plan, the study delivers a more focused approach to how the US Navy might best and most effectively incorporate these unmanned systems. Though the UUV Master Plan document is, admittedly, quite out of date (the study itself now more than six years old), the findings therein are still highly relevant to the discussion surrounding the future of unmanned technologies beneath the waves.

Working with the very limited data available on UUVs, the authors of the study considered the technical issues inherent in developing and fielding unmanned underwater systems. Though the full complement of UUV hardware and software is considered in the study, for brevity’s sake this publication review will focus only on two technical factors: autonomy and communications. Intuitively, some missions (such as those of a clandestine or sensitive nature) demand more autonomy than others (like infrastructure monitoring or environmental surveillance). Pertaining to ISR missions, the study suggested that vehicle autonomy limitations would be a significant limiting factor.   AUVs may not, for instance, be able to effectively determine what collected information is time-critical and what information is not. This potential weakness could be a tremendous risk; either the notional AUV would fail to transmit information in a timely manner or it would transmit non-useful information needlessly, risking detection and sacrificing stealth. Without significant development, therefore, lack of autonomy would present a technical challenge and, for some advocated missions, an operational risk.  In the words of the authors “autonomy and bandwidth form a trade-space in which onboard autonomy is traded for reach-back capability and visa-versa.” The study also addressed perhaps the most frequently cited criticism of UUV technologies: communications and connectivity. Submerged UUVs, the study concludes, are limited in their ability to communicate by “the laws of physics,” while surfaced UUV’s ability to communicate are limited by technology (mast height, data output rates) and present yet another trade-off between stealth and connectivity. These communication systems are, in the words of the authors, considered mature, and are unlikely to be significantly improved by additional research and development.

It’s important to note (and probably obvious to readers) that development of technologies to address the challenges of autonomy and communication for UUV platforms are likely completely opaque to this author. The study’s findings, however, seem to match the challenges the US Navy is facing developing UUVs in the years after its publication. The Office of Naval Research’s Large Displacement Unmanned Underwater Vehicle (LDUUV) program awarded a $7.3 million contract to Metron Inc. to develop and field autonomy software, hardware, and sensors. The LDUUV, a pier-launched system, intended for endurance missions of more than seventy days, will need to effectively avoid interference, requiring a high degree of autonomy. A 2011 Office of Naval research brief envisioned that the LDUUV would “enable the realization of fully autonomous UUVs operating in complex near shore environments” concurrent with the development of “leap ahead” technologies in autonomy.  In November of 2014, ONR unveiled a plan to develop an ASW mission package for the LDUUV, pursuing technology development in mission autonomy, situational awareness, and undersea sensors, with emphases on software-in-the-loop and hardware-in-the-loop simulations, and other ASW mission package components. Whether or not intensive R&D will produce the degree of “leap ahead” autonomy necessary for such operations remains to be seen. In the meantime, however, the RAND study’s recommended UUV missions are of particular interest and may dictate the application of funding in a time of scarcity. Put another way, the study’s conclusions provide a cogent and clear roadmap for what the US Navy can do with UUVs as they are and will reasonably become, not how it would like them or envision them to be.

LDUUV Prototype
LDUUV Prototype

So, then, there is the million (multi-billion?) dollar question: what missions are practically and cost-effectively best suited for UUVs, given these limitations, especially if a mismatch between desired technical functionality and funding and actual ability and allotments continues? The authors suggest (in concurrence with CIMSEC’s own Chris Rawley) that UUV technologies are first and foremost best suited for mine countermeasures, followed in priority by missions to deploy leave-behind sensors, near-land or harbor monitoring, oceanography, monitoring undersea infrastructure, ASW tracking, and inspection/identification in an ATFP or homeland defense capacity. These recommendations are based on already-proven UUV capabilities, cost-effectiveness, and demand. UUVs performing these missions, in particular MCM, have seen steady and

Conceptualization of the Knifefish SMCM UUV System
Conceptualization of the Knifefish SMCM UUV System

encouraging progress in the years since the study’s publication. NATO’s Center for Maritime Research and Exploration (CMRE) collected and analyzed data from four UUVs with high-resolution sonar deployed during Multinational Autonomy Experiment (MANEX) 2014. The Littoral Combat Ship’s (LCS) mine-hunting complement includes a pair of Surface Mine Countermeasures (SMCM) UUVs, dubbed Knifefish, that uses its low-frequency broadband synthetic aperture side-scanning sonar to look for floating, suspended, and buried mines and an onboard processor to identify mines from a database. The way ahead for longer-term missions demanding greater autonomy and reach-back over long distances is, for the time being, less clear.

This publication review is truly a very (very!) cursory glance at an incredibly detailed, highly technical study, and in no way does justice to the breadth and depth of the document.  I encourage interested readers to download the original .pdf.  However, the study’s contributions to an overall understanding of how and where UUVs can practically and cost-effectively support naval operations are significant, effectively reckoning the need to develop cutting-edge technologies with sometimes harsh but ever-present operational and financial realities. UUVs will undoubtedly have a significant role in the undersea battle-space in the years to come; RAND’s 2009 study provides keen insight into how that role may develop.

Lethal Autonomy in Autonomous Unmanned Vehicles

Guest post written for UUV Week by Sean Welsh.

Should robots sink ships with people on them in time of war? Will it be normatively acceptable and technically possible for robotic submarines to replace crewed submarines?

These debates are well-worn in the UAV space. Ron Arkin’s classic work Governing Lethal Behaviour in Autonomous Robots has generated considerable attention since it was published six years ago in 2009. The centre of his work is the “ethical governor” that would give normative approval to lethal decisions to engage enemy targets. He claims that International Humanitarian Law (IHL) and Rules of Engagement can be programmed into robots in machine readable language. He illustrates his work with a prototype that engages in several test cases. The drone does not bomb the Taliban because they are in a cemetery and targeting “cultural property” is forbidden. The drone selects an “alternative release point” (i.e. it waits for the tank to move a certain distance) and then it fires a Hellfire missile at its target because the target (a T-80 tank) was too close to civilian objects.

Could such an “ethical governor” be adapted to submarine conditions? One would think that the lethal targeting decisions a Predator UAV would have to make above the clutter of land would be far more difficult than the targeting decisions a UUV would have to make. The sea has far fewer civilian objects in it. Ships and submarines are relatively scarce compared to cars, houses, apartment blocks, schools, hospitals and indeed cemeteries. According to the IMO there are only about 100,000 merchant ships in the world. The number of warships is much smaller, a few thousand.

Diagram of the ethical governer
Diagram of the ‘ethical governor’

There seems to be less scope for major targeting errors with UUVs. Technology to recognize shipping targets is already installed in naval mines. At its simplest, developing a hunter-killer UUV would be a matter of putting the smarts of a mine programmed to react to distinctive acoustic signatures into a torpedo – which has already been done. If UUV were to operate at periscope depth, it is plausible that object recognition technology (Treiber, 2010) could be used as warships are large and distinctive objects. Discriminating between a prawn trawler and a patrol boat is far easier than discriminating human targets in counter-insurgency and counter-terrorism operations. There are no visual cues to distinguish between regular shepherds in Waziristan who have beards, wear robes, carry AK-47s, face Mecca to pray etc. and Taliban combatants who look exactly the same. Targeting has to be based on protracted observations of behaviour. Operations against a regular Navy in a conventional war on the high seas would not have such extreme discrimination challenges.

A key difference between the UUV and the UAV is the viability of telepiloting. Existing communications between submarines are restricted to VLF and ELF frequencies because of the properties of radio waves in salt water. These frequencies require large antenna and offer very low transmission rates so they cannot be used to transmit complex data such as video. VLF can support a few hundred bits per second. ELF is restricted to a few bits per minute (Baker, 2013). Thus at the present time remote operation of submarines is limited to the length of a cable. UAVs by contrast can be telepiloted via satellite links. Drones flying over Afghanistan can be piloted from Nevada.

For practical purposes this means the “in the loop” and “on the loop” variants of autonomy would only be viable for tethered UUVs. Untethered UUVs would have to run in “off the loop” mode. Were such systems to be tasked with functions such as selecting and engaging targets, they would need something like Arkin’s ethical governor to provide normative control.

DoD policy directive 3000.09 (Department of Defense, 2012) would apply to the development of any such system by the US Navy. It may be that a Protocol VI of the Convention on Certain Conventional Weapons (CCW) emerges that may regulate or ban “off the loop” lethal autonomy in weapons systems. There are thus regulatory risks involved with projects to develop UUVs capable of offensive military actions.

Even so, in a world in which a small naval power such as Ecuador can knock up a working USV from commodity components for anti-piracy operations (Naval-technology.com, 2013), the main obstacle is not technical but in persuading military decision makers to trust the autonomous options. Trust of autonomous technology is a key issue. As Defense Science Board (2012) puts it:

A key challenge facing unmanned system developers is the move from a hardware-oriented, vehicle-centric development and acquisition process to one that addresses the primacy of software in creating autonomy. For commanders and operators in particular, these challenges can collectively be characterized as a lack of trust that the autonomous functions of a given system will operate as intended in all situations.

There is evidence that military commanders have been slow to embrace unmanned systems. Many will mutter sotto voce: to err is human but to really foul things up requires a computer. The US Air Force dragged their feet on drones and yet the fundamental advantages of unmanned aircraft over manned aircraft have turned out to be compelling in many applications. It is frequently said that the F-35 will be the last manned fighter the US builds. The USAF has published a roadmap detailing a path to “full autonomy” by 2049 (United States Air Force, 2009).

Similar advantages of unmanned systems apply to ships. Just as a UAV can be smaller than a regular plane, so a UUV can be smaller than a regular ship. This reduces requirements for engine size and elements of the aircraft that support human life at altitude or depth. UAVs do not need toilets, galleys, pressurized cabins and so on. In UUVs, there would be no need to generate oxygen for a crew and no need for sleeping quarters. Such savings would reduce operating costs and risks to the lives of crew. In war, as the Spanish captains said: victory goes to he who has the last escudo. Stress on reducing costs is endemic in military thinking and political leaders are highly averse to casualties coming home in flag-draped coffins. If UUVs can effectively deliver more military bang for less bucks and no risk to human crews, then they will be adopted in preference to crewed alternatives as the capabilities of vehicles controlled entirely by software are proven.

Such a trajectory is arguably as inevitable as that of Garry Kasparov vs Deep Blue. However in the shorter term, it is not likely that navies will give up on human crews. Rather UUVs will be employed as “force multipliers” to increase the capability of human crews and to reduce risks to humans. UUVs will have uncontroversial applications in mine counter measures and in intelligence and surveillance operations. They are more likely to be deployed as relatively short range weapons performing tasks that are non-lethal. Submarine launched USVs attached to their “mother” subs by tethers could provide video communications of the surface without the sub having to come to periscope depth. Such USVs could in turn launch small UAVs to enable the submarine to engage in reconnaissance from the air.  The Raytheon SOTHOC (Submarine Over the Horizon Organic Capabilities) launches a one-shot UAV from a launch platform ejected from the subs waste disposal lock . Indeed small UAVs such

AeroVironment Switchblade UUV
AeroVironment Switchblade UUV

as Switchblade (Navaldrones.com, 2015) could be weaponized with modest payloads and used to attack the bridges or rudders of enemy surface ships as well as to increase the range of the periscope beyond the horizon. Future aircraft carriers may well be submarine.

In such cases, the UUV, USV and UAV “accessories” to the human crewed submarine would increase capability and decrease risks. As humans would pilot such devices, there are no requirements for an “ethical governor” though such technology might be installed anyway to advise human operators and to take over in case the network link failed.

However, a top priority in naval warfare is the destruction or capture of the enemy. Many say that it is inevitable that robots will be tasked with this mission and that robots will be at the front line in future wars. The key factors will be cost, risk, reliability and capability. If military capability can be robotized and deliver the same functionality at similar or better reliability and at less cost and less risk than human alternatives, then in the absence of a policy prohibition, sooner or later it will be.

Sean Welsh is a Doctoral Candidate in Robot Ethics at the University of Canterbury. His professional experience includes  17 years working in software engineering for organizations such as British Telecom, Telstra Australia, Fitch Ratings, James Cook University and Lumata. The working title of Sean’s doctoral dissertation is “Moral Code: Programming the Ethical Robot.”

References

 Arkin, R. C. (2009). Governing Lethal Behaviour in Autonomous Robots. Boca Rouge: CRC Press.

Baker, B. (2013). Deep secret – secure submarine communication on a quantum level.   Retrieved 13th May, 2015, from http://www.naval-technology.com/features/featuredeep-secret-secure-submarine-communication-on-a-quantum-level/

Defense Science Board. (2012). The Role of Autonomy in DoD Systems. from http://fas.org/irp/agency/dod/dsb/autonomy.pdf

Department of Defense. (2012). Directive 3000.09: Autonomy in Weapons Systems.   Retrieved 12th Feb, 2015, from http://www.dtic.mil/whs/directives/corres/pdf/300009p.pdf

Navaldrones.com. (2015). Switchblade UAS.   Retrieved 28th May, 2015, from http://www.navaldrones.com/switchblade.html

Naval-technology.com. (2013). No hands on deck – arming unmanned surface vessels.   Retrieved 13th May, 2015, from http://www.naval-technology.com/features/featurehands-on-deck-armed-unmanned-surface-vessels/

Treiber, M. (2010). An Introduction to Object Recognition: Selected Algorithms for a Wide Variety of Applications. London: Springer.

United States Air Force. (2009). Unmanned Aircraft Systems Flight Plan 2009-2047.   Retrieved 13th May, 2015, from http://fas.org/irp/program/collect/uas_2009.pdf