Assessing 9/11 Lessons and the Way Ahead for Homeland Defense Against Small Unmanned Aerial Systems

Peter L. Hickman, Major, United States Air Force, holds a PhD from Arizona State University in International Relations and a Master of Military Operational Art and Science in Joint Warfare. He is currently a Defense Legislative Fellow for a member of the House Armed Services Committee. Prior to this position, he worked as a Requirements Manager on Air Combat Command HQ staff and the Chief of Weapons and Tactics at the 225th Air Defense SquadronThe views expressed in this paper represent the personal views of the author and are not necessarily the views of the Department of Defense or of the Department of the Air Force.  Divergent Options’ content does not contain information of an official nature nor does the content represent the official position of any government, any organization, or any group.

Title:  Assessing 9/11 Lessons and the Way Ahead for Homeland Defense Against Small Unmanned Aerial Systems

Date Originally Written:  March 18, 2020.

Date Originally Published:  May 13, 2020.

Author and / or Article Point of View:  The author is a field-grade, U.S. Air Force Weapons Officer who has worked in homeland air defense for the past 8 years at tactical and headquarters levels. He is currently a Defense Fellow assigned to the office of a member of the House Armed Services Committee. The article is written from the point of view of an American strategic analyst viewing the emerging threat of small unmanned systems in the context of the current state of North American air defense.

Summary:   For small unmanned aerial systems (sUAS), the current state of North American air defense is analogous to its state prior to the 9/11 attacks, and therefore the risk posed by an sUAS attack is currently high. However, the lessons of 9/11 for adapting air defense to a new class of threat provides a model to prepare for the threat of sUAS before an attack occurs.

Text:  The beginning of the twenty first century has seen rapid development of small unmanned aerial systems (sUAS). Violent extremist organizations and others with malign intent have already demonstrated the threat posed by sUAS in attacks overseas. Though a successful attack has not yet occurred in North America, current limitations of the North American air defense system suggest that chances of defeating one when it does occur are very low. However, the hard lessons of the 9/11 attacks provide a model for proactive measures that will enable effective defense if an sUAS attack occurs in North America.

The first documented non-state use of an sUAS as an improvised explosive device (IED) in an attack was by Hezbollah in 2006[1]. More recently, Houthi fighters in Yemen have used sUAS to damage radar systems[2], and the Islamic State and other groups have used sUAS to drop small explosives on forces on the ground, at one point even resulting in the halt of a U.S. ground force advance on Mosul[3]. Rebels in Ukraine used an sUAS to destroy an arms depot resulting in damage that has been estimated as high as a billion dollars[4]. The first documented fatalities from sUAS attacks occurred in 2016 when two Kurdish fighters were killed, and two members of French special operations forces were wounded by an sUAS-based IED[5]. There are also reports from as far back as 2014 of fatal non-state sUAS attacks[6].

The proven lethal potential of sUAS attacks is not limited to far off battlefields. sUAS attacks on North America have already been foiled by intelligence and law enforcement organizations in 2011 and 2015, and gaps in security were demonstrated when an sUAS was inadvertently flow over the White House in January of 2015[7]. Even more alarming incidents have taken place in Europe and Japan, including a 2013 demonstration against German Chancellor Angela Merkel where an sUAS was flown onto the stage where she was speaking[8]. Another bizarre incident found an sUAS on the roof of the Prime Minister of Japan’s house that was “marked with radioactive symbols, carried a plastic bottle with unidentifiable contents, and registered trace levels of radiation[9].

Systems are currently available that can provide point defense against sUAS for a small area for a limited time. These systems are effective for some military applications overseas as well as providing limited point defense for specific events and facilities in North America. However, a point defense approach is not effective for extending the existing air defense system of North America to include wide area defense against sUAS. This lack of effectiveness is because the current North American air defense system was originally designed to defend against state actors and was updated in the aftermath of 9/11 to defend against manned aircraft attacks that originate from within the U.S.. Though the current system is not postured to provide effective wide area defense against sUAS, the changes that were made just after 9/11 provide a model for urgently needed changes.

Immediately following the 9/11 attacks, North American air defense was adapted in three main ways: increased domain awareness, interagency coordination, and additional defeat measures. Immediately post-9/11, NORAD & NORTHCOM gained access to interior Federal Aviation Administration (FAA) radars and radios which enabled the domain awareness capabilities that were lacking on 9/11. Interagency coordination tactics, techniques, and procedures were developed so that the FAA could notify air defense tactical units within seconds of detection of concerning flight behavior. Finally, a widespread constellation of alert aircraft and other defeat measures was established that would enable persistent timely response to any event in the national airspace. The net result of the post-9/11 changes to air defense was not to eliminate the risk entirely of a successful air attack, but to mitigate that risk to an acceptable level.

These post-9/11 measures are effective for mitigating the risk of the last attack, but they will not be for the next. The legacy radar systems providing surveillance for air defense were designed to detect manned aircraft at typical transit altitudes and are not well suited to targets that are small, slow, and low in altitude. The federal air traffic management procedures that form the basis of effective interagency coordination aren’t yet in place for sUAS. Though simple restrictions on operating areas exist, the lack of a comprehensive sUAS traffic management plan means that the FAA does not have the tools that would enable timely notification of suspicious sUAS activity. Finally, existing alert bases and response options assume that targets will be moving on manned aircraft scales, measured in hundreds of miles, which means that the existing constellation of alert bases and response postures are well situated to defend major population centers and critical assets from manned aircraft. sUAS operate on scales that render this existing approach ineffective, both in terms of the times and distances required to make an intercept, but also in terms of the size of the aircraft, which are very difficult for manned pilots to acquire with onboard systems, and almost impossible to visually acquire while traveling as much as ten times faster than the target.

Without effective domain awareness, interagency coordination, or defeat measures, relative to sUAS, North American air defense is in a state analogous to pre-9/11. Fortunately, the lessons learned on 9/11 provide a model of what is now required to anticipate the next attack, though the details will be different. The unique characteristics of sUAS suggest that sensor coverage volumes may not need to be as comprehensive as they are above 18,000 feet, and existing and emerging sensors can be augmented with sophisticated data analysis to better report sUAS detections that today are dismissed as radar noise. The framework for broad interagency coordination exists today, but lacks specific tactics, techniques, and procedures tailored to communicating an unfolding sUAS threat. The decreased ranges of sUAS potentially enable much better target envelope predictions which translates to much more tightly focused interagency coordination and rapid, targeted risk mitigation for any threat. Modest hardening and warning-based shelter-in-place or evacuation can provide a much larger measure of risk mitigation than they can against a hijacked airliner or cruise missile, which likely reduces the need for exquisite defeat mechanisms.

Though the existing North American air defense system is not well position to defeat an sUAS attack, the lessons of 9/11 suggest that adaptation of our current system to mitigate risk of sUAS attack may be closer we think. There are near term opportunities to weave a tailored blend of increased domain awareness, interagency coordination, and defeat measures to enable risk mitigation specific to the threat of a small sUAS. The only question now is whether this adaptation takes place before, or after, the first sUAS attack in the homeland.


[1] Ash Rossiter, Drone Usage by Militant Groups: Exploring Variation in Adoption, Defense & Security Analysis 34, no. 2 (April 3, 2018): 116,

[2] Ibid, 116.

[3] Ibid, 117.

[4] Ibid, 117.

[5] Ibid, 116.

[6] Ibid, 117.

[7] Ryan Wallace and Jon Loffi, Eamining Unmanned Aerial System Threats & Defenses: A Conceptual Analysis, International Journal of Aviation, Aeronautics, and Aerospace, 2015, 1,

[8] Ibid, 1.

[9]Ibid, 2.

Assessment Papers Homeland Defense Peter L. Hickman United States Unmanned Aerial Systems