Loitering munition

A loitering munition (also known as a suicide drone[1][2][3][4] or kamikaze drone[5][6][7]) is a weapon system category in which the munition loiters around the target area for some time, searches for targets, and attacks once a target is located.[8][9][10] Loitering munitions enable faster reaction times against concealed or hidden targets that emerge for short periods without placing high-value platforms close to the target area, and also allow more selective targeting as the actual attack mission can be aborted.

Loitering munitions fit in the niche between cruise missiles and unmanned combat aerial vehicles (UCAVs) sharing characteristics with both. They differ from cruise missiles in that they are designed to loiter for a relatively long time around the target area, and from UCAVs in that a loitering munition is intended to be expended in an attack and has a built-in warhead.

Loitering weapons first emerged in the 1980s for use in the Suppression of Enemy Air Defenses (SEAD) role against surface-to-air missiles (SAMs), and were deployed for the SEAD role in a number of military forces in the 1990s. Starting in the 2000s, loitering weapons have been developed for additional roles ranging from relatively long-range strikes and fire support down to tactical, very short range battlefield systems that fit in a backpack.

Loitering munitions have proliferated into use by at least 14 countries, with several different types in use as of 2017. The rising proliferation and the ability to use some systems as lethal autonomous weapons coupled with ethical concerns over such use have led to research and discussion by International humanitarian law scholars and activists.


First development and terminology

Initially, loitering munitions were not referred to as such but rather as suicide UAVs or loitering missiles. Different sources point at different projects as originating the weapon category. The early 1980s initial Israeli Delilah variants[11][12] or the failed US AGM-136 Tacit Rainbow program[13][14] are mentioned by some sources. Alternatively, the late 1980s IAI Harpy which was widely exported is considered by some as the first loitering munition system.[15]

Early projects did not use the "loitering munition" nomenclature which emerged at a much later date, and used existing terminology at the time. For instance the AGM-136 Tacit Rainbow was described as follows in a 1988 Air Force Magazine article:

the Tacit Rainbow unmanned jet aircraft being developed by Northrop to loiter on high and then swoop down on enemy radars could be called a UAV, a cruise missile, or even a standoff weapon. But it is most definitely not an RPV.

Initial role in suppression of enemy air defense

The response to the first generation of fixed installation surface-to-air missiles (SAMs) such as SA-2 and SA-3 was the development of the anti-radiation missile such as AGM-45 Shrike and other means to attack fixed SAM installations, as well as developing SEAD doctrines. The Soviet counter-response was the use of mobile SAMs such as SA-6 with intermittent use of radar.[16] Thus, the SAM battery was only visible for a small period of time, during which it was also a significant threat to high-value Wild Weasel fighters. In 1982 Operation Mole Cricket 19 various means including UAVs and air-launched Samson decoys were used over suspected SAM areas to saturate enemy SAMs and to bait them to activate their radar systems, which were then attacked by anti-radiation missiles.[17][18]

In the 1980s, a number of programs, such as the IAI Harpy or the AGM-136 Tacit Rainbow, integrated anti-radiation sensors into a drone or missile air frames coupled with command and control and loitering capabilities. This allowed the attacking force to place relatively cheap munitions in place over suspected SAM sites, and to attack promptly the moment the SAM battery is visible. This integrated the use of a drone as a baiting decoy with the attack role into one small and relatively cheap platform in comparison to the alternative wild weasel jet fighter.[19][20][21][22]

Evolution into additional roles

Starting in the 2000s, loitering weapons have been developed for additional roles beyond the initial SEAD role ranging from relatively long-range strikes and fire support[23] down to tactical, very short-range battlefield use such as the AeroVironment Switchblade which is deployed at the platoon level and fits in a backpack.[24][25][26][27] A documented use of loitering munitions was in 2016 Nagorno-Karabakh clashes in which an IAI Harop was used against a bus functioning as a troop transport.[28]


Loitering munitions may be as simple as an unmanned aerial vehicle (UAV) with attached explosives that is sent on a potential kamikaze mission, and may even be constructed with off the shelf commercial quadcopters with strapped on explosives.[29]

Purpose built munitions are more elaborate in flight and control capabilities, warhead size and design, and on-board sensors for locating targets.[30] Some loitering munitions use a human operator to locate targets whereas others, such as IAI Harop, can function autonomously searching and launching attacks without human intervention.[31][32]

Some loitering munitions may return and be recovered by the operator if they are unused in an attack and have enough fuel; in particular this is characteristic of UAVs with a secondary explosive capability.[33] Other systems, such as Delilah[11][34] or IAI Harop,[10] don't have a recovery option and are self-destructed in mission aborts.

Comparison to similar weapons

Loitering munitions fit in the niche between cruise missiles and unmanned combat aerial vehicles (UCAVs).[10][35]

The following table compares similar size-class cruise missiles, loitering munitions, and UCAVS:

CharacteristicCruise missileLoitering munitionUCAV
Cost appropriate for expendable one-time useYesYesNo, but high cost allows for higher-quality platform
Recovery possible after launchNoUsually noYes, typical mission profile is round-trip
Built-in warheadYesYesNo
Stealthy final dive to targetUsually yesUsually yesUsually no
LoiteringNo or limitedYesUsually yes
Sensors for target acquisitionLimitedYesUsually yes
command and control during flightUsually limitedYesYes
RangeLonger, optimized for constant speed flightShorterShorter, even shorter for typical round-trip mission
SpeedTypically higherTypically lowerDepends on role
Example type
Range1,600 km1,000 km1,100 km
Max speedhigh sub-sonic, 880 km/h190 km/h217 km/h
Flight endurancec. 2 hours6 hours24 hours
Engine3.1 kilonewtons (700 lbf) F107-WR-402 turbofan engine37 hp Wankel engine115 hp Rotax 914F
Loaded system weight1,588 kg135 kg1,020 kg
Payload450 kg warhead23 kg warhead2 × AGM-114 Hellfire or 6 × AGM-176 Griffin air-to-surface missiles
Length6.25 m2.5 m8.22 m
Wingspan2.67 m [36]3.0 m [30]16.8 m [37]

Whereas some cruise missiles, such as the block IV Tomahawk, have the ability to loiter and have some sensory and remote control features,[38] their primary mission is typically strike and not target acquisition. Cruise missiles, as their name implies, are optimized for long-range flight at constant speed both in terms of propulsion systems and wings or lifting body design. They are often unable to loiter at slow fuel-efficient speeds which significantly reduces potential loiter time even when the missile has some loiter capabilities.[39]

Conversely almost any UAV could be piloted to crash onto a target and most could be fitted with an improvised explosive warhead.[29] However the primary use of a UAV or UCAV would be for recoverable flight operations carrying reconnaissance equipment and/or munitions. While many UAV designs are explicitly designed with loitering in mind, they are not optimized for a diving attack often lacking forward facing cameras, lacking in control response-speed which is unneeded in regular UAV flight, and are noisy when diving at the target potentially providing warning to the target. UAV's, being designed as multi-use platforms, often have a unit cost that is not appropriate for regular one-time expendable mission use.[40][35]

The primary mission of a loitering munition is reaching the suspected target area, target acquisition during a loitering phase, followed by a self-destructive strike, and the munition is optimized in this regard in terms of characteristics (e.g. very short engine life time, silence in strike phase, speed of strike dive, optimization toward loitering time instead of range/speed) and unit cost (appropriate for a one-off strike mission).[41][42]

Ethical and international humanitarian law concerns

Loitering munitions that are capable of making autonomous attack decisions (man out of the loop) raise moral, ethical, and international humanitarian law concerns because a human being is not involved in making the actual decision to attack and potentially kill humans, as is the case with fire-and-forget missiles in common use since the 1960s. Whereas some guided munitions may lock-on after launch or may be sensor fuzed, their flight time is typically limited and a human launches them at an area where enemy activity is strongly suspected, as is the case with modern fire-and-forget missiles and airstrike planning. An autonomous loitering munition, on the other hand, may be launched at an area where enemy activity is only probable, and loiter searching autonomously for targets for potentially hours following the initial launch decision, though it may be able to request final authorization for an attack from a human. The IAI Harpy and IAI Harop are frequently cited in the relevant literature as they set a precedent for an aerial system (though not necessarily a precedent when comparing to a modern naval mine) in terms of length and quality of autonomous function, in relation to a cruise missile for example.[43][44][45][46][47][48]

Users and producers

As of 2017, loitering munitions are in use in several countries, including:

See also


  1. US army may soon use Israeli-designed ‘suicide drones’, Jerusalem Post, June 2016
  2. China Unveils a Harpy-Type Loitering Munition, Israel Defense, March 2017
  3. Meet Israel’s ‘Suicide Squad’ of Self-Sacrificing Drones, The Drive, August 2016
  4. Loitering Munitions - In Focus, Center for the Study of the Drone, Feb 2017
  5. Kamikaze drone loiters above, waits for target, CNET, June 2009
  6. 'Kamikaze drones' add a new layer of lethality to remote force, C4ISRNET, August 2015
  7. Israeli-made kamikaze drone spotted in Nagorno-Karabakh conflict, Washington Post, April 2016
  8. Loitering Munition Availability Expanding Internationally, Aviation Week, April 2016
  9. Loitering Weapon Systems – A Growing Demand, h-ils, December 2016
  10. Watch This Drone Turn Into A Missile, Popular Science, August 2015
  11. The Secrets of Delialah (Hebrew), IAF bulletin, issue 184, December 2008
  12. Loitering Weapons are making a Comeback, Defense Update, June 2009
  13. An Introduction to Autonomy in Weapon Systems, pages 13-14, By: Paul Scharre and Michael C. Horowitz, CNAS Working paper, Feb 2015
  14. Canan, James W. "Unmanned Aerial Vehicles." Air Force Magazine (1988)., page 87
  15. Drone Strike!: UCAVs and Aerial Warfare in the 21st Century, By Bill Yenne, ISBN 9781580072526, pages 106-107
  16. Reedy, Edward K. (1 January 1987). "Radar ECCM Considerations and Techniques". In Eaves, Jerry L.; Reedy, Edward K. (eds.). Principles of Modern Radar. Springer US. pp. 681–699. doi:10.1007/978-1-4613-1971-9_22. ISBN 978-1-4612-9170-1.
  17. Six Days in June (Hebrew), IAF bulletin, issue 145, June 2002
  18. Surface to Air Missile Effectiveness in Past Conflicts, Technical Report APA-TR-2010-1001, Dr Carlo Kopp, AFAIAA, SMIEEE, PEng, October 2010
  19. Meet Israel's 'Suicide Squad' of Self-Sacrificing Drones, August 2016, The Drive
  20. ADAPTIVE DISCRETE EVENT SIMULATION FOR ANALYSIS OF HARPY SWARM ATTACK, Brandon J. Cobb, Naval Postgraduate School, Thesis, September 2011
  21. "Suminsby, Robert E. Fear no Evil: Unmanned combat air vehicles for suppression of enemy air defenses. AIR UNIV MAXWELL AFB AL AEROSPACE STUDIES INST, 2002".
  22. Loitering, Smart Cruise Missile Marketed to U.S. Navy, National Defense, June 2001
  23. British Army Sets to Deploy Fire Shadow Loitering Weapons to Afghanistan by Early 2012 Defense Update, September 2011
  24. Military Investigates Killer Drones That Can Fit in Rucksacks National Defense, July 2011
  25. A Tiny Missile That Waits Overhead—Silent, Patient and Deadly, WarIsBoring, January 2014
  26. AeroVironment producing Switchblade missiles for Army UPI, October 2016
  27. Loitering Autonomous Weapons, Defense Update, January 2007
  28. Israeli-made kamikaze drone spotted in Nagorno-Karabakh conflict, Washington Post, April 2016
  29. ISIS Using Kamikaze Drones in Iraq, Popular Mechanics, October 2016
  30. iClean – Loitering Attack UCAV, Artzi Dror, Technion Institute of Technology, 2012
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  32. Harpy Air Defense Suppression System, Defense Update, 2006
  33. IAI's ROTEM – Tactical Multirotor Killer Drone, Defense Update, 2016
  34. Delilah – The IAF Loitering Missile, Defense Update, June 2009
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  36. RGM/UGM-109 Tomahawk, fi-aeroweb, November 2014
  37. MQ-1B Predator factsheet, US Air Force, July 2010
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