Introduction
The proliferation of small unmanned aerial systems (sUAS), also known colloquially as “drones” has drastically expanded in recent years. SUAS are widely utilized by hobbyists for purposes such as aerial photography/videography and competitive racing events. Additionally, sUAS are widely used for commercial purposes (such as media, agriculture, and mapping/surveying), as well as government purposes (to include law enforcement and firefighting). However, threat actors utilizing sUAS also pose a unique force protection concern for Department of Defense (DoD) installations. This paper will examine potential threat actor uses of sUAS, as well as an overview of sUAS characteristics and capabilities. This paper will then examine the legal framework and various capabilities available to counter potential sUAS threats. Finally, the paper will detail DoD-specific sUAS case studies, as well as additional examples of sUAS threat activity from around the world.

sUAS Threat Overview
Threat actors may seek to utilize sUAS for activities for a variety of malicious purposes. Individuals seeking to collect intelligence on DoD facilities or operations could use sUAS (and associated cameras/sensors) to gather imagery/video and other information. Terrorist actors (both foreign and domestic) could utilize sUAS to carry a weaponized payload (such as explosives or chemical/biological agents). Individuals intent on interfering with aviation operations could fly sUAS near airfields or testing/training ranges in order to disrupt or potentially damage aircraft. Furthermore, protestors opposing the DoD could utilize sUAS for various messaging efforts, for harassment, or to collect imagery/video in furtherance of their causes.

The nature of modern sUAS platforms allows for significant standoff distance, which can allow threat actors to conduct malicious activities from off-installation locations which may be more difficult to identify and/or access. This complicates security forces’ ability to identify and apprehend malicious sUAS operators. Additionally, it should be noted that even non-malicious actors (such as a young or misinformed sUAS operator) could have similar effects on operations as a malicious actor. Security forces responses and other protective measures could be implemented following an sUAS incursion, temporarily disrupting operations regardless of the sUAS operator’s intent.

sUAS Capabilities
The DoD classifies UAS into five groups based on maximum gross takeoff weight (MGTW), normal operating altitude, and airspeed. Group one is the smallest UAS with an MGTW of 20 pounds or less, normal operating altitude of 1,200 ft and airspeed less than 100 knots. Group 2 has an MGTW of 55 pounds or less, fitting the FAA definition of sUAS, with a normal operating altitude of less than 3,500 feet and airspeed of less than 250 knots. Group 3 has an MGTW of less than 1,320 pounds, operating altitude of less than 18,000 ft and an airspeed of less than 250 knots. DoD considers groups 1-3 as sUAS, although group 3 has significantly greater capabilities and would generally be operated by government agencies or commercial enterprises. This white paper will focus on groups one and two with an MGTW of 55 pounds or less.1,2

The sUAS market is growing rapidly. There are more than 600 manufacturers producing over 1,700 different systems built for purposes which include recreational, imaging, disaster response, agriculture, mining, research prototypes, and military applications. The majority of sUAS platforms are fixed wing or rotorcraft with a small minority of platforms being a hybrid design or lighter than air design. Most rotorcraft sUAS are multicopter designs. Hobbyist sUAS are the easiest to procure and provide threat actors the most anonymity when making the purchase. More capable sUAS can be found at high-end hobby shops and industrial suppliers. These purchases are more expensive, require more interpersonal contact and involve record keeping requirements which complicate and may deter threat actors from purchasing these systems. With the proliferation of online communities, do-it-yourself sUAS are being built by hobbyists. Online sources educate builders on designs, and where to purchase components and systems from online retailers. 3D printing technology including metals and composite materials, allows the construction of airframes and other sUAS parts with designs being available on the internet. These custom built sUAS offer threat actors increased anonymity in procurement while allowing them to design and build sUAS to fit their specific needs.3,4

Rotary-wing battery electric sUAS make up approximately 41% of the total sUAS variants currently on the market. The most commonly purchased sUAS variants have a mean endurance of 21 minutes, mean maximum range of 1.8 miles, and mean payload weight of 4.6 lbs. While this represents the capability of the most likely sUAS that may be encountered it is worth noting that hybrid-wing hybrid-propulsion sUAS platforms have a range of up to 419 miles and endurance of up to 520 minutes. These hybrid platforms have fixed wing surfaces that produce lift along with quadrotor multicoptor rotors. Rotary-wing internal platforms that use internal combustion engines have the highest mean payload of 13.6 pounds. While these platforms are less likely to be utilized by a threat actor, they represent the most dangerous platforms due to their increased capabilities. Advances in battery technology including Li-Metal, Flow and Solid-State batteries could double sUAS endurance and range as early as 2028.3

Other types of sUAS exist that are uncommon but may present viable options for threat actor use. Powered parachute sUAS use a propeller while a parachute produces lift, just like manned paraplanes. Inexpensive and easy to control, these sUAS are easily deployed and can be packed into very small spaces for transport. There are some tiltrotor sUAS designs that operate like the U.S. military’s V-22 Osprey. These provide vertical take off and landing capability while possessing fixed wing speed and endurance. Lighter than air sUAS operate much like a blimp and radio-controlled blimps are easily converted into this type of sUAS. Although they operate at low speed, they are capable of long endurance.3

The command, control and communication capabilities of sUAS are also developing rapidly. Drones are no longer fully dependent on human input for their controls for all aspects of flight. Many sUAS platforms have proven capable of path-following, follow-me, obstacle avoidance, small-team coordination, and swarm formations. Path-following, sometimes referred to as self-flying or autopilot, requires the sUAS operator to pre-program the flight path, often using waypoints to adjust altitude, direction and speed. Follow-me flight uses remote control bracelets or a phone app that emits a global navigation satellite (GNSS) signal for the sUAS to follow. Some sUAS with high quality visual sensors can track an object or person that has been selected in the user interface. Small-team coordination and swarm formations require pre-programmed flight patterns and is basically a complex version of path-following control. All of these types of flight are precursors to fully autonomous sUAS flight where the machine itself is capable of adaptive autonomous control. The rapid growth of Artificial Intelligence (AI) will likely aid and hasten the development of such flight technologies. Autonomous flight capability removes the requirement of a signal to control the aircraft making it radio silent and much more difficult to detect and intercept.3,5

Frequencies used to control sUAS are relatively broad and multiple frequencies are required to control the sUAS in flight, broadcast telemetry and communicate with any potential payload. Most sUAS are controlled on spread-spectrum bands such as 2.4 gigaherz (GHz), 5.8 GHz and other GHz bands that offer significantly reduced interference and detectability. Controlling sUAS using 3G, 4G, or 5G cell phone signals is also possible. Although this form of control is more likely to have lag in the control response, using cell phone signals makes detecting the source of the signal more difficult as it is mixed in with normal cell phone transmission traffic. Some sUAS can be controlled by satellite communications (SATCOM). SATCOM options are currently limited and expensive making their use by threat actors less likely. However, projects such as OneWeb and Space X’s Starlink are building microsatellite constellations that will reduce the cost of SATCOM and reduce the latency of the signals.3

The rapid proliferation and miniaturization of various technologies give sUAS sensing payloads significant capabilities that could be exploited by threat actors. Sensing payload types can include:

• Still and Video Cameras: Current cameras are capable of 4k resolution, however communication bandwidth generally limits real time image transmission to 2k resolution. Some cameras are so small and lightweight that a second payload can be carried on some sUAS. Infrared (IR) cameras are less common and more expensive, however their use in agriculture and other industries makes them readily available. The capability of still and video cameras give threat actors the ability to gather images and information at greater distance and in low light conditions.3
• Light Detection and Ranging (LIDAR): LIDAR allows for highly accurate 3D imaging and measuring. There are multiple commercial applications making this technology available albeit expensive. Highly accurate 3D imaging produced by LIDAR can be used for mapping, determining line of sight, target tracking and detection, and navigation including the autonomous navigation of unmanned vehicles.3,6
• Hyperspectral Sensing: Hyperspectral sensing is becoming more widely used in agriculture for their ability to inspect crops quickly and accurately, providing information on soil quality, water stress and early detection of crop diseases. Hyperspectral sensing can simultaneously collect hundreds of narrow and contiguously spaced spectral bands of data including visible light, near infrared, shortwave infrared, mediumwave infrared and longwave infrared radiation. Not all Hyperspectral cameras can cover his entire range of the spectrum. In military applications, Hyperspectral sensing can be used to support reconnaissance, surveillance, and targeting. It can also be used for defensive purposes as it can detect threats from incoming missiles to chemical agents.3
• Radar: Miniaturized radar systems as small as 1.65 lbs with a three (3) km range. Developments in autonomous flight are causing changes in regulations which now require radar navigation of aircraft in certain situations. This will likely drive further research and development into the miniaturization of radar making it more suitable for use on sUAS.3
• Electronic Intelligence (ELINT): The freedom of movement and agility of sUAS make them a superb platform for cataloging electronic signals. This collection could be passive, active, or possibly the disruption or spoofing of electronic signals.3
• Electronic Jamming: Radio Frequency (RF) electronic payloads could be used to jam air traffic control signals as well as Global Positioning Satellite (GPS) and Global Navigation Satellite (GNSS). The mobility of sUAS gives the threat actor the ability to affect receivers over a wider area than a ground-based jammer. Although the use of this technology is illegal in the U.S., jammers as small as a few inches long and weighing only a few ounces can be purchased on the internet.3
• Acoustic Sensors: Currently, the use of acoustic sensors is mainly theoretical, but work is being done to develop the ability of acoustic sensors to detect obstacles and other sUAS to aid in autonomous flight.3
• Radiation Sensors: sUAS have been fitted with radiation sensors to detect gamma, X-ray, alpha and beta particle radiation.3

Non-sensing payloads carried by sUAS range from propaganda leaflets, nuisance and noisemaking devices, illegal drugs, conventional weapons and chemical, biological, radiological, or nuclear (CBRN) weapons. Below are examples of payload delivery methods:

• Kamikaze / Suicide / One-Way Attack Drone: An explosive payload is attached to the sUAS and both the payload and UAS are crashed into the target. Most often, there is an associated video feed allowing the sUAS to gather information prior to selecting the target.3
• Payload Release: Releasable payloads vary depending upon the mission. Explosive devices, often hand grenades and small mortars are used to conduct kinetic attacks. Cyber-enabled devices (such as Wi-Fi sniffers) and unmanned ground sensors can be released, increasing the reconnaissance and surveillance capability of sUAS. Illegal narcotics, weapons, or other contraband can be flown over borders and released at predetermined drop points.3
• Sprayers: Lawful use of sprayers for commercial and agricultural use is growing. Threat actors could use this type of delivery method for attacks utilizing chemical or biological agents.3

Counter-UAS Legal Framework
The legal environment surrounding counter-UAS (C-UAS) capability employment is in its early stages and continues to evolve. With DoD installations located worldwide, it is important to note that legal frameworks vary by jurisdiction.
Within the United States, the DoD’s C-UAS efforts are largely governed by Chapter 3 of U.S. Code Title 10, Section 130i. Section 130i authorizes DoD installations “to take certain actions with respect to unmanned aircraft systems, including using reasonable force to disable, damage, or destroy them.” While the exact DoD policies authorizing such actions remain classified, Section 130i mentions specific “covered facilities or assets” which may warrant protection. These facilities/assets must be “identified by the Secretary of Defense,” must be “located in the United States (including the territories and possessions of the United States)” and must relate to various national security missions, to include “nuclear command and control, integrated tactical warning and attack assessment, and continuity of government; the missile defense mission of the Department; or the national security space mission of the Department.”7

In host nation environments where the DoD has installations/assets located outside of U.S. jurisdiction, legalities regarding C-UAS vary widely. Per the DoD’s 2021 Counter-Small Unmanned Aircraft Systems Strategy, “host nation environments have a diverse array of statutes and regulations that could inhibit effective force protection efforts.” The Strategy further notes that “[DoD] bases and operations in host nations must work with local airspace control authorities while complying with local laws and obligations of treaties or other agreements.”8

In contingency environments where DoD personnel are forward-deployed and engaging in active military operations, C-UAS legalities defer toward the laws of war and self-defense. Per the aforementioned 2021 DoD Strategy, “contingency locations are generally the least restrictive operating environment but potentially carry the highest risk.” Since active hostilities may be present, commanders will ensure that appropriate roles of engagement are utilized for C-UAS issues.

Counter-sUAS Capabilities
Counter-sUAS (C-sUAS) systems are specifically designed for the detection, tracking, identification, and defeat of group one (1) and two (2) sUAS. Several technologies including radar, RF scanners, electro-optical sensors and infrared cameras are commonly used for detection. Options to defeat sUAS include jamming sUAS RF control or payload links, jamming sUAS GNSS signals, or kinetic attacks such as lasers, projectiles, or interception with another sUAS. The most effective fixed site systems use multiple detection methods, increasing the likelihood of detection and have multiple defeat methods giving commanders and operators more options based on circumstances. Mobile systems generally have limited detection and defeat methods, but can provide C-sUAS capability during movement, in austere environments, and fill gaps not covered by fixed site systems.9,10

Detection of sUAS systems is difficult due to the myriad of factors involved. Differences in sUAS size, speed, transmission frequencies, and operational environments impact the effectiveness of the different sensors used by C-sUAS systems. Sensor types include electro-optical/infrared (EO/IR), ELINT, acoustics and LIDAR. Each has a range of capabilities with unique strengths and weaknesses, and all can have issues with false alarms based on the environment in which they are deployed.3

• Radar: The effectiveness of radar as a detection method is dependent upon the shape, surface material and motion of the object the radar is attempting to detect. Many sUAS are being built with plastics and carbon-based materials for their strength, flexibility, and reduced weight. However, these materials can reduce an objects radar signature. Doppler radars can separate moving target signatures from other background clutter. Rotor blades used on sUAS produce unique Doppler signatures that can aid in detection and identification. As sUAS control and navigation capabilities improve, threat actors may have more ability to use terrain to mask the movement of sUAS, particularly in crowded urban environments. Radars with wider bandwidths, advance digital signal processing and agility with respect to frequency and waveform are likely to be the most effective for the detection of sUAS.3,11
• EO/IR Sensors: Like radar, EO/IR sensors are affected by atmospheric effects, and the shape, surface material and motion of the object the sensor is attempting to detect. These sensors operate at much higher frequencies in the electromagnetic domain and generally fall into two broad classes, imaging and non-imaging.
  • Imaging Sensors: These sensors can create still or full motion images to detect, identify and track targets depending on the resolution of the sensor. Imaging sensors have a smaller field of view and are most effective when being cued by other detection sensors.3
  • Non-imaging Sensors: These sensors do not have the resolution required to produce an image. However, they can detect and track targets as point targets. The advantage is the increased field of view allowing for more efficient searches of larger areas. Battery powered sUAS have lower radiant intensities than internal combustion or jet powered counterparts making them more difficult to decipher from the environment by non-imaging sensors. Reduced battery temperature can improve battery life, providing incentive for manufacturers to use cooler batteries, leading to reduced thermal signatures in the future for sUAS.3
• ELINT Sensors: ELINT sensors passively detect signals of interest emitted from both the controller and the sUAS. Signal identification relies on prior knowledge of the signal of interest. ELINT sensors use digital libraries containing waveform parameters of threat emitters. When a signal is detected, it is compared to the signals in the library for identification. If a threat actor uses a signal not in the library of the ELINT sensor it will be ignored. ELINT sensors can also produce false alarms from other emitters such as wireless hotspots or GoPro cameras. While one ELINT sensor can provide relatively accurate bearing to the source of the signal, multiple ELINT sensors can work together to triangulate a signal. The more sensors and wider angular spread increase the accuracy of location finding capability. ELINT sensors can be largely defeated by reducing signals emitted. This can be accomplished by sUAS flying preplanned routes and recording data onboard the sensor instead of transmitting data. Threat actors can also use decoy sUAS or swarming techniques to overwhelm ELINT sensors. Lastly, the use of cell signal controls make ELINT detection difficult as the signals are mixed amongst other cell signals.3
• Acoustic Sensors: These sensors are most effective at closer ranges as sound power decreases by six (6) decibels for each doubling of distance between the source and receiver. There is market demand for quieter sUAS systems, particularly for commercial use in urban areas. As a result, C-UAS manufacturers are beginning to turn away from acoustic sensors as a primary method of detection.3
• LIDAR Sensors: These sensors use pulsed laser light to illuminate a target and then collect the reflected pulses to accurately measure distance to target. LIDAR sensors typically use ultraviolet, visible or near-IR light to illuminate targets. LIDAR sensors can quickly and precisely locate targets, providing range and azimuth during both day and night. LIDAR is also very effective at separating targets from other foreground and background clutter. Atmospheric conditions such as rain, fog and haze negatively affect LIDAR because of the two-way transmission of the pulsed lasers. When used near people, the maximum laser power should be limited to make the lasers eye-safe, decreasing its potential capability. Research has indicated that LIDAR has the ability to detect sUAS at ranges out to 30 meters. Future research and development being conducted is likely to make LIDAR more effective C-sUAS option in the future.3

Since each of the above sensors have different strengths and weaknesses, a “system of systems” approach to C-sUAS is likely to provide the most effective results. This is especially true for installations where fixed site systems can be employed and tailored to the environment and potential threats. Since all systems produce false alarms, training of operators and technicians is critical to the overall effectiveness of the systems.3

Case Study: NAS JRB Fort Worth
At Naval Air Station (NAS) Joint Reserve Base (JRB) Fort Worth in Texas, leadership has expressed concerns regarding the installation’s encounters with unauthorized sUAS in their airspace. Open-source reporting indicates that drone reports have increased from approximately 100 encounters to more than 300 monthly. In addition, including sUAS maneuvering through their airspace multiple times, the installation has reported more than 700 incidents a month. According to a former Commanding Officer of NAS JRB Fort Worth, most observed drone operators are younger individuals unintentionally flying recreationally in the area. However, these unauthorized sUAS are considered hazardous for aircraft at NAS JRB Fort Worth, as there have been two (2) incidents in which DoD aircraft had to maneuver around unauthorized drones to avoid a crash. Furthermore, a crash in September 2021 involving a bird flying into an aircraft’s engine, which damaged three (3) houses in the Lake Worth neighborhood, highlights the potential damage unauthorized objects pose to NAS JRB Fort Worth’s single-engine aircraft.12

While the former Commanding Officer indicated that leadership does not believe the unauthorized drone flights in NAS JRB Fort Worth’s airspace demonstrate “hostile intent,” sUAS in the vicinity of the installation could pose potential surveillance concerns. NAS JRB Fort Worth hosts dozens of units, including the Air Force’s 301st Fighter Wing. In January 2021, the Secretary of the Air Force named the 301st Fighter Wing, NAS JRB Fort Worth, the first Air Force Reserve Command F-35 unit-equipped wing. According to the press release announcing the decision, the F-35s are being assembled at the Fort Worth Lockheed Martin Plant, across the runway from the 301st Fighter Wing. At the time of the announcement, the wing was expected to receive the first F-35A aircraft in summer 2024, replacing its aging fleet of F-16 Fighting Falcons. In November 2023, a few F-35s with interim software flew for the first time at NAS JRB Fort Worth. Any unauthorized sUAS surveillance into the production or testing of F-35s (which are designed with stealth technology, advanced aerodynamic performance and integrated avionics to bolster U.S. air dominance) could potentially disrupt U.S. defense advantages.13,14,15,16

Case Study: NAVBASE Kitsap
Naval Base (NAVBASE) Kitsap is the third largest U.S. Navy installation in the United States. It is home to all types of U.S. Navy submarines, two Nimitz-class aircraft carriers, Puget Sound Naval Shipyard and the largest fuel depot in the Continental U.S. NAVBASE Kitsap is located on the Kitsap Peninsula, approximately 20 miles West-Northwest of Seattle, WA and is composed of multiple installations including Puget Sound Naval Shipyard, Naval Submarine Base Bangor, Keyport Underwater Warfare Center, Naval Hospital Bremerton and the Manchester Fuel Depot. The sensitive and strategic nature of NAVBASE Kitsap makes foreign intelligence activities a legitimate concern. After repeated flights of private drones over these installations, the U.S. Navy requested the Kitsap County Board of Commissioners pass legislation to prevent such flights. On 10 September 2019, Ordinance 571-2019 went into effect, requiring operators to notify the U.S. Navy in advance of UAS operations within 3000 feet of these installations. Notification is made through an online form located on the Kitsap County website. Requirements include the location, time, drone description, FAA registration number and contact information of the operator.17

While the FAA continues to adapt regulations regarding recreational and commercial operation of sUAS to fit the rapid growth of technology, their efforts cannot address the specific concerns of individual military installations. A myriad of factors including the environment around an installation, civilian encroachment, signals encroachment, installation and tenant missions, and the equipment and technology aboard the installation must all be taken into account when determining the risk associated with sUAS operations near an installation. The communication and cooperation between Naval Base Kitsap and the Kitsap County government is a good example of how installations can partner with local governments to mitigate the threats associated with sUAS while balancing the rights of law-abiding citizens. C-sUAS programs are bolstered by such efforts because they provide insight to the installation on expected honest and legal use of sUAS in the area, making identification of potential threat actor use of sUAS easier.

Additional Examples
There have also been a number of significant sUAS kinetic attacks across the Middle East. Installations across Syria and Iraq as well as U.S. Navy warships in the Red Sea have been targeted numerous times since the beginning of the Israel-Hamas war on 07 October 2023.18

Open-source reporting on the attacks against U.S. interests in Iraq and Syria indicate the majority of attacks involved drones, indirect fires (rockets or mortars), or a combination of the two. Very little reporting on the types of drones used is available, however two sUAS systems identified in the attacks were the Qasef-2K and the Shahed-101. The Qasef-2K is an Iranian attack drone with a range of 150 km, endurance of two (02) hours, ceiling of 9,800 feet and can carry a 66-pound payload. The Shahed-101 is a larger Iranian attack drone with a delta wing design. It is usually guided by a preprogrammed flight path to a predetermined target, eliminating the need for a constant control signal and reducing it’s ELINT signature. This design has been copied by Russia and China and has been used often by Russia against Ukraine. Some of these variants have been observed with carbon fiber components and a black coating. These changes are likely attempts to reduce the radar signature and engine heat signature.19,20,21

Houthi rebels in Yemen have also utilized one-way attack drones to target merchant ships in the Red Sea shipping lanes. While information on what types of drones are being used to carry out these attacks, two of the most common one-way attack drones used by the Houthi’s are the KAS-04 and the Shahed-136. The KAS-04 is produced at by Iran’s Kimia Part Sivan Company, has a range of 1,700 km. The Shahed-136 is also Iranian produced and is a loitering munition or suicide / kamikaze drone capable of drone swarm attacks with a range estimated between 1,000 km and 2,500 km.18

Hamas used multirotor sUAS to great effect during their 07 October 2023 attack on Israel. The majority of these sUAS would be categorized as Group two (02) sUAS by DoD standards. Small explosive munitions were dropped on Israeli border security towers which housed cameras, communication and machine gun emplacements. One video released by Hamas shoed a commercially available quadcopter attacking an Israeli tank. Targets deeper into Israeli territory were attacked with larger one-way attack drones of various types.22

The contrast between the kinetic attacks conducted using Group two (02) and Group three (03) sUAS show the limited capability for kinetic attacks by the smaller Group two (02) sUAS. However, kinetic attacks by smalls sUAS can be highly effective when coordinated against softer targets such as camera systems and communications equipment. Even an attack on a main battle tank can render the electro-optical sighting systems and communications equipment inoperable, making the tank significantly less effective. Group three (03) sUAS carry larger, more powerful payloads over much larger distances making them more effective in kinetic attacks against larger targets. Technology is being applied to make them more difficult to detect by C-UAS systems, further increasing their lethality. In depth study of these sUAS attacks across the Middle East, along with the wars in Ukraine and Azerbaijan is critical for the future of C-UAS systems to keep up with emerging technology.

Outlook
The widespread proliferation of sUAS will continue to pose a force protection challenge for the DoD. Threat actors will almost certainly continue to utilize sUAS for malicious activities around the world, to include areas with a DoD presence. While there is currently limited publicly available evidence suggesting a specific sUAS threat to the DoD outside of active conflict zones, the continued evolution of sUAS systems and ongoing challenges regarding C-UAS legal frameworks and C-sUAS capabilities creates an environment conducive to future threat activity. RMC’s Intelligence & Climate Analysis Division continues to monitor relevant developments related to threat actor use of sUAS platforms, as well as potential threats to DoD installations, assets, and personnel worldwide.

Sources

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22. Jankowicz, Mia. (2023, October 10). How Hamas likely used rudimentary drones to ‘blind and deafen’ Israel’s border and pave the way for its onslaught. Business Insider. Retrieved from https://www.businessinsider.com/hamas-drones-take-out-comms-towers-ambush-israel-2023-10.