Loitering munition

A loitering munition (also known as a suicide drone,^[1][2][3][4] kamikaze drone,^[5][6][7] or exploding drone)^[8] is a kind of aerial weapon with a built-in munition (warhead), which can loiter (wait passively) around the target area until a target is located; it then attacks the target by crashing into it.^[9][10][11] Loitering munitions enable faster reaction times against hidden targets that emerge for short periods without placing high-value platforms near the target area and also allow more selective targeting as the attack can be changed mid-flight or aborted.

Loitering munitions fit in the niche between cruise missiles and unmanned combat aerial vehicles (UCAVs or combat drones), 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. As such, they can also be considered a nontraditional ranged weapon.

An Iranian HESA Shahed 136 long range loitering munition

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 in that role with a number of military forces in the 1990s. Starting in the 2000s, loitering weapons were 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.

History

First development and terminology

Northrop AGM-136 Tacit Rainbow on display at the National Museum of the U.S. Air Force in Dayton, Ohio

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 failed US AGM-136 Tacit Rainbow program^[12][13] or the 1980s initial Israeli Delilah variants^[14][15] are mentioned by some sources.^[16] The Iranian Ababil-1 was produced in the 1980s but its exact production date is unknown.^[17] The Israeli IAI Harpy was produced in the late 1980s.^[16]

IAI Harpy first-generation loitering munition for SEAD role

Early projects did not use the "loitering munition" nomenclature, which emerged much later; they used terminology existing at the time. For instance the AGM-136 Tacit Rainbow was described in a 1988 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

Loitering Munitions HERO (UVision Air Ltd, Israel), DSEI 2019, London

The response to the first generation of fixed installation surface-to-air missiles (SAMs) such as S-75 and S-125 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 2K12 Kub with intermittent use of radar.^[18] 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 Israel's 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.^[19][20]

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.^{[21][22][23][24]}

Evolution into additional roles

XM501 US prototype capable of launching LAM (loitering attack munition)

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^[25] down to tactical, very short-range battlefield use.^{[26][27][28][29]} A documented use of loitering munitions was in the 2016 Nagorno-Karabakh conflict in which an IAI Harop was used against a bus being used as a troop transport for Armenian soldiers.^[7] HESA Shahed 136 and the ZALA Lancet have been used by Russia in the ongoing Russian invasion of Ukraine, while Ukraine has fielded loitering munitions such as the American-made AeroVironment Switchblade, which is deployed at the platoon level and fits in a backpack.

During conflicts in the 2010s and 2020s, conventional armies and non-state militants alike began modifying common commercial racing drones into an FPV loitering munition by the attachment of a small explosive, so-named because of the first-person view (FPV) they provide the operator. Explosive ordnance such as an IED, grenade, mortar round or an RPG warhead are fitted to an FPV drone then deployed to aerial bomb tactical targets. FPV drones also allow direct reconnaissance during the drone's strike mission.^[30][31]

After the Russian invasion of Ukraine began in 2022, both Russian and Ukrainian forces were producing thousands of FPV drones every month by October 2023, many of which were donated by volunteer groups.^[32] Escadrone Pegasus and the Vyriy Drone Molfar are two examples of the low-cost drones that rapidly evolved in 2022–23 during the war.^[33] On 9 November 2023, Ukrainian soldiers claimed to have used a civilian-donated FPV drone to destroy a Russian Tor missile system on the Kupiansk front, showcasing the potential cost-effectiveness of fielding such munitions. A Tor missile system costs some $24 million dollars to build, which could buy 14,000 FPV drones.^[34][35]

Characteristics

Air-launched Delilah loitering munition, controlled by backseat WSO

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.^[36]

Purpose-built munitions are more elaborate in flight and control capabilities, warhead size and design, and onboard sensors for locating targets.^[37] 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.^[38][39] Another example is UVision HERO solutions – the loitering systems are operated remotely, controlled in real time by a communications system and equipped with an electro-optical camera whose images are received by the command and control station.^[40][41]

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.^[42] Other systems, such as the Delilah^[14][43][11] don't have a recovery option and are self-destructed in mission aborts.

Countermeasures

Russia uses the ZALA Lancet drones in Ukraine. Since spring 2022 Ukrainian forces have been forced to build cages around their artillery pieces using chain link fencing, wire mesh and even wooden logs as part of the construction. One analyst told Radio Liberty that such cages were “mainly intended to disrupt Russian Lancet munitions.” A picture supposedly taken from January 2023 shows the rear half of a Lancet drone that failed to detonate due to such cages. Likewise Ukrainian forces have used inflatable decoys and wooden vehicles, such as HIMARS, to confuse and deceive Lancet drones.^[44][45]

Ukrainian soldiers report shooting down Russian drones with sniper rifles.^[46] Russian soldiers use electronic warfare to disable or misdirect Ukrainian drones and have reportedly used the Stupor anti-drone rifle, which uses an electromagnetic pulse that disrupts a drone's GPS navigation.^[47] A Royal United Services Institute study in 2022 found that Russian Electronic Warfare units, in March and April 2022, knocked out or shot down 90% of Ukrainian drones that they had at the start of the war in February 2022. The main success was in jamming GPS and radio links to the drones.^[48]

Russian tanks have been fitted with rooftop slat armor at the beginning of the Russian invasion of Ukraine which could provide protection against loitering munitions in some circumstances. Some Ukrainian tanks taking part in the 2023 Ukrainian counteroffensive were also spotted using roof screens.^{[49][50] [51]}

Comparison to similar weapons

Loitering munitions fit in the niche between cruise missiles and unmanned combat aerial vehicles (UCAVs).^[11][52]

The following table compares similar size-class cruise missiles, loitering munitions, and UCAVS:^{[citation needed]}

Characteristic	Cruise missile	Loitering munition	UCAV
Cost appropriate for expendable one-time use	Yes	Yes	No, but high cost allows for higher-quality platform
Recovery possible after launch	No	Usually no	Yes, typical mission profile is round-trip
Built-in warhead	Yes	Yes	No
Stealthy final dive to target	Usually yes	Usually yes	Usually no
Loitering	No or limited	Yes	Usually yes
Sensors for target acquisition	Limited	Yes	Usually yes
Command and control during flight	Usually limited	Yes	Yes
Range	Longer, optimized for constant speed flight	Shorter	Shorter, even shorter for typical round-trip mission
Speed	Typically higher	Typically lower	Depends on role
Example type	Block IV Tomahawk cruise missile. Its small wing area is optimized for high-speed cruise.	center|IAI Harop, a loitering munition optimized for the Suppression of Enemy Air Defenses (SEAD) role	center|General Atomics MQ-1 Predator UCAV
Range	1,600 km	1,000 km	1,100 km
Max speed	high sub-sonic, 880 km/h	190 km/h	217 km/h
Flight endurance	c. 2 hours	6 hours	24 hours
Engine	3.1 kilonewtons (700 lbf) F107-WR-402 turbofan engine	37 hp (28 kW) Wankel engine	115 hp (86 kW) Rotax 914F
Loaded system weight	1,588 kg	135 kg	1,020 kg
Payload	450 kg warhead	23 kg warhead	up to 204 kg (2 × AGM-114 Hellfire or 6 × AGM-176 Griffin air-to-surface missiles)
Length	6.25 m	2.5 m	8.22 m
Wingspan	2.67 m [53]	3 m [37]	16.8 m [54]

Whereas some cruise missiles, such as the Block IV Tomahawk, have the ability to loiter and have some sensory and remote control features,^[55] 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.^[56]

Conversely almost any UAV could be piloted to crash onto a target and most could be fitted with an improvised explosive warhead.^[36] However the primary use of a UAV or UCAV would be for recoverable flight operations carrying reconnaissance equipment and/or munitions. While many UAVs 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, 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.^[57][52]

NCSIST Chien Hsiang, an example of an expendable loitering munition

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).^[58][59]

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.^{[60][61][62][63][64][65]}

List of users and producers

(As of 2023), loitering munitions are used by the armed forces of several countries, including:

•  Argentina – HERO 30, HERO 120^[66]
•  Armenia – HRESH, BEEB 1800,^[67] AW21^[68]
•  Australia – Drone 40^[69]
•  Azerbaijan – IAI Harpy, IAI Harop, Orbiter 1K,^[7] SkyStriker, STM Kargu,^[70][71] Qirği, Quzgün^[72]
•  Belarus – UBAK-25 Chekan^[73]
•  Brazil – Anshar^[74]
•  China – IAI Harpy, CH-901, WS-43, ASN-301^[75][76]
•  Greece – Attalus,^[77] Aihmi AHM-1X^[78]
•  Indonesia – Rajata^[79]
•  India – IAI Harpy, IAI Harop,^[80][81] SkyStriker, Warmate, Trinetra, Nagastra series, ALS-50,^[82] JM-1, Sierra Tango
•  Iran – Shahed 131, Shahed 136 (loitering capabilities disputed),^[83][84] Hesa Ababil-2, Raad 85, Arash-2, Meraj-521, Meraj-532, Zhubin, Shahin-1,Shahed 238 and possibly others^{[85][86][87][88]}
•  Israel – IAI Harpy, IAI Harop, IAI Harpy NG, IAI Green Dragon, IAI Rotem L, Orbiter 1K,^[89] Delilah, SkyStriker,^[90][91] Spike Firefly, HERO loitering munitions series,^{[92][93][94][95]} Viper,^[96] Lanius,^[97] Point Blank,^[98] SpyX,^[99] and upgraded variants.^[100]
•  Lithuania – Switchblade^[101]
•  Morocco – IAI Harop
•  Poland – WB Electronics Warmate^[102]
•  Portugal – UAVision Elanus^[103]
•  Russia – KUB-BLA ("Cube"), ZALA Lancet,^{[104][105][106]} Geran-1, Geran-2
•  Serbia – Gavran^[107], Osica^[108], Komarac^[109], Vila 1^[110]
•  Singapore – IAI Harop
•  Slovakia – AX-2 Predator
•  South Africa – Paramount N-Raven^[111]
•  South Korea – Devil Killer,^[112][113] IAI Harpy
•  Spain - Q-SLAM-40
•  Sudan – Kamin-25
•  Taiwan – NCSIST Chien Hsiang,^[114] NCSIST Fire Cardinal
•  Turkey Robit UAV AZAB,^[115] – IAI Harpy,^[116] STM Kargu,^[117] STM Alpagu,^[118] Transvaro-Havelsan Fedai,^[119] LENTATEK Kargı,^[120] Roketsan-STM Alpagut^[121][122]
•  Turkmenistan – SkyStriker
•  UAE – QX-1,^[123][124] Hunter SP,^[125] Hunter 2-S,^[126][127] Hunter 5, Hunter 10,^[128] Shadow 25, Shadow 50,^[129][130] RW-24,^[131] N-Raven^[132]
•  United Kingdom – Switchblade
•  United States – AeroVironment Switchblade, Phoenix Ghost, Raytheon Coyote,^[133] HERO 120, Point Blank, ALTIUS-600M.
•  Ukraine – RAM II, Switchblade, ST-35 Silent Thunder, Phoenix Ghost, Warmate, Bober, AQ-400 Scythe, UJ-25 Skyline
•  Yemen – (Houthis) – Qasef-1/2K,^[134] Shahed 131, Shahed 136, Samad-2/3

See also

• Flying bomb
• XM501 Non-Line-of-Sight Launch System
• Boeing Persistent Munition Technology Demonstrator
• Low Cost Autonomous Attack System
• Sypaq Corvo Precision Payload Delivery System
• Television guidance
• V-1 flying bomb

References

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