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
warhead that is typically designed to
loiter around a target area until a target is located, then attack 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.
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
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]
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.
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
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
UJ-25 Skyline or 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
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] do not 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 building 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]
Both Ukraine and Russia rely on electronic warfare to defeat FPV drones. Such jammers are now used on Ukrainian trenches and vehicles.[49] Russian forces have built jammers that can fit into a backpack.[50] And now pocket size jammers exist for soldiers.[51] As of June 2023 Ukraine was losing 5-10,000 drones a month, or 160 per day, according to
Ukrainian soldiers. Previously they could fly their drones for kilometres, now they are lucky if they can get 500 metres in the air.[52]
This has led to Russia creating wire guided FPV drones, similar to a
wire-guided missile or even wire guided torpedoes. One drone captured by Ukrainian forces had "nearly seven miles (just over 10.8 kilometers)" of fibre optic cable. Such guidance would make the link between operators and FPV drone immune to jamming. It would also allow for much faster updates from the drone. However these drones would lack the manoeuvrability that wireless drones enjoy.[53] Ukraine has also responded by using autonomous drones tasking to ensure that a jammed drone can hit a target. In March 2024 footage put on social media showed a Ukrainian FPV drone being jammed just before it struck a target. Despite the loss of operator control it still managed to strike the target.[54]
On 21 March 2024, recent footage of the submarine Tula showed that it has been fitted with a
'cope cage' to prevent drone strikes, the first ocean going asset to carry such a modification.[58]
Comparison to similar weapons
Loitering munitions fit in the niche between cruise missiles and unmanned combat aerial vehicles (UCAVs).[11][59]
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
Whereas some cruise missiles, such as the
Block IV Tomahawk, have the ability to loiter and have some sensory and remote control features,[62] 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.[63]
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.[64][59]
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 lifetime, 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).[65][66]
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.[67][68][69][70][71][72]
List of users and producers
As of 2023[update], loitering munitions are used by the armed forces of several countries, including: