Loitering munition

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.[28]

Purpose built munitions are more elaborate in flight and control capabilities, warhead size and design, and on-board sensors for locating targets.[29] 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.[30][31]

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.[32] Other systems, such as Delilah[11][33] or IAI Harop,[10] don't have a recovery option and are self-destructed in mission aborts.

Loitering munitions fit in the niche between cruise missiles and unmanned combat aerial vehicles (UCAVs).[10][34]

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

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. Small wing area is optimized for high-speed cruise.	IAI Harop a loitering munition optimized for the Suppression of Enemy Air Defenses (SEAD) role	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 Wankel engine	115 hp Rotax 914F
Loaded system weight	1,588 kg	135 kg	1,020 kg
Payload	450 kg warhead	23 kg warhead	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 [35]	3.0 m [29]	16.8 m [36]

Whereas some cruise missiles, such as the block IV Tomahawk, have the ability to loiter and have some sensory and remote control features,[37] 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.[38]

Conversely almost any UAV could be piloted to crash onto a target and most could be fitted with an improvised explosive warhead.[28] 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.[39][34]

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).[40][41]

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.[42][43][44][45][46][47]

As of 2020, loitering munitions are in use in several countries, including:

•  Azerbaijan - IAI Harpy, IAI Harop, Orbiter 1K[7]
•  China - IAI Harpy, CH-901, WS-43, ASN-301[48][49]
•  Germany,[50]
•  India,[51]
•  Iran - Qasef-1, Raad 85 (UAV), and possibly others[52][53][54]
•  Islamic State of Iraq and the Levant - organized program of acquiring commercial drones, and improvising them for loitering munition role[28][55][56]
•  Israel - IAI Harpy, IAI Harop, IAI Green Dragon, IAI Rotem L, Aeronautics Defense Orbiter, Delilah, SkyStriker.[57] Indigenous manufacture of additional types by Israel Aerospace Industries,[58] UVision,[59][60] Aeronautics Defense,[61] Elbit Systems,[62] and Israel Military Industries[63]
•  Kazakhstan,[4]
•  Poland - WB Electronics Warmate[64]
•  South Korea - Devil Killer,[65][66] IAI Harpy
•  Taiwan - NCSIST Chien Hsiang,[67] NCSIST Fire Cardinal
•  Turkey[68] IAI Harpy STM Kargu STM ALPAGU[69] TOGAN
  

  Main Loitering munition of Turkish Armed Forces, IAI Harpy
•  United States - AeroVironment Switchblade, Raytheon Coyote[70]
•  Uzbekistan[4] - IAI Harpy, IAI Harop
•  Yemen Houthis Rebels - Qasef-1[71]

• XM501 Non-Line-of-Sight Launch System
• Boeing Persistent Munition Technology Demonstrator
• Low Cost Autonomous Attack System