Uzi Rubin
The precision of Iranian-made suicide UAVs, combined with their cheapness, has turned them into a potent weapon on the battlefields of Ukraine.
The appearance of Iran’s Shahed 131/136 unmanned aerial vehicles (UAVs) in Ukraine has catapulted them to the centre of global attention and generated numerous papers by military observers and analysts. Yet audiences in the Middle East have been familiar with them ever since their operational debut in Saudi Arabia. In September 2019, two major Saudi oil installations, Abqaiq and Khurais, were heavily damaged by swarms of UAVs, supposedly launched by Houthi insurgents in retaliation for the Kingdom’s intervention in the Yemen civil war. A few days later, debris from the attacking UAVs was exhibited in a press conference convened by the Saudi Armed Forces spokesperson. The debris included a hitherto unknown delta wing UAV powered by a small rotary engine (aka Wankel motor) driving a wooden propeller. Labelled by the Saudis as ‘Unknown Delta Wing UAV’, it was the first evidence of a secret Iranian UAV programme, apparently considered a game changer by the Islamic Republic.
The origins of the Shahed 131/136 are quite obscure. Iran’s armed forces have been acquiring and deploying indigenous UAVs ever since the Iran–Iraq war in the 1980s. Numerous types of new UAVs are routinely displayed in the annual military parades the Iranian regime loves to hold. They also feature prominently in various military exhibitions, each one being described and extolled by the eager military correspondents of Iran’s state-controlled media. Yet the ‘Unknown Delta Wing UAV’ was nor exhibited prior to the September 2019 attack on the Saudi oil installations, nor did it appear for some considerable time after that attack. Five years before that attack, in December 2014, Iran’s Mashregh News Agency featured 10 types of UAVs that could be used for suicide missions. One of them, called ‘Touphan’ (‘Typhoon’), which was described as being capable of ‘locating and destroying the enemy by using an optical tracker’, could ‘approach the enemy from various points and because of its high speed it is difficult for the enemy to react in time. The drone is constructed of lightweight radar-absorbing materials and has a small radar cross section… a front-facing camera in the nosecone transmits live images until the moment of impact’. This description was accompanied by an image of a delta wing UAV, very similar to the ‘Unknown Delta Wing UAV’ that struck Saudi Arabia almost five years later. Significantly, the ‘Touphan’ was never displayed again by Iran.
In this sole exposure in Iran's media, the ‘Touphan’ was described as having a speed of 250 km/hr and an endurance of one hour. In contrast, the ‘Unknown Delta Wing UAVs’ from September 2019 flew at least several hundred kilometres before hitting the Abqaiq oil facility, and no optical sensors were found among their debris. If the ‘Touphan’ was indeed the progenitor of the weapon used in the Saudi attacks, it has been modified considerably since its previous appearance in 2014, from a short-range loitering munition to a long-range suicide UAV – for all practical purposes a propeller-driven cruise missile.
Why did the Iranians keep this weapon under a veil of secrecy for almost half a decade? Perhaps they perceived it as a game changer, reserving it for a strategic surprise, which they achieved in their Pearl Harbour-like sneak attack on Saudi Arabia's major oil installations.
Another possible explanation has to do with their policy vis-à-vis the war in Yemen. The Houthi insurgents, fighting Saudi Arabia since the latter's intervention in the civil war, are fully supported by Iran. This support includes the supply of rockets, missiles and UAVs, which are used to attack Saudi military, industrial and civilian infrastructure deep inside the Kingdom's territory. However, a UN Security Council resolution from 2015 forbids shipment of armaments to the warring sides in the Yemen civil war. To distance themselves from the illegal arming of their Houthi allies, the Iranians maintain the fiction that all the Houthi missiles and UAVs are of indigenous design and production. To maintain this fiction, the Iranian ballistic missiles smuggled in sections to the Houthis are rebranded and repainted. The Iranian-designed and supplied UAVs that strike inside Saudi Arabia are seldom shown in Iranian colours or used by Iran's armed forces. Since the September 2019 attack on the Saudi oil installations was supposedly launched from Yemen and employed only ‘Yemeni indigenous’ UAVs, any disclosure of the true Iranian provenance of the ‘Unknown Delta Wing UAV’ would risk condemnation of Iran as the true perpetrator of this attack and as being in breach of the UN Security Council-imposed arms embargo on the warring sides in Yemen.
The next appearance of the still-unnamed ‘Unknown Delta Wing UAV’ in the limelight came almost two years later. On 21 July 2021, the Japanese-owned but Israeli-operated oil tanker Mercer Street was struck by an unknown UAV, killing its British captain and his Romanian bodyguard. The ship was hit while on its way towards the port of Fujaira, near the Straits of Hormuz. From witness reports, several attempts to strike the ship failed on the preceding day, and the successful hit on 21 July was preceded by a previous failed attack. Examination of the debris of the UAV found on the deck of the Mercer Street revealed that it was identical to the ‘Unknown Delta Wing UAV’ from the September 2019 Saudi attack. How this feat of hitting a moving target was achieved remains a mystery. Usually, hitting a moving target requires some kind of homing system, which in turn requires an onboard sensor – optical or otherwise. Yet, as in the case of the Saudi attack, no sensor was mentioned in the report on the examination of the debris.
The Shahed 136's simplicity, combined with its almost uncanny accuracy, long range and low cost, makes it unique among strategic standoff weapons
The nameless ‘Unknown Delta Wing UAV’ finally acquired a name in September 2021, when Israel's then Prime Minister Naftali Bennett disclosed the existence of an Iranian long-range UAV dubbed Shahed 136, branding it as a menace to Israel and other moderate states in the Middle East. He specifically linked this UAV to the 2019 attack on the Saudi oil installations. Shortly afterwards, in December 2021, the Iranians finally unveiled the Shahed 136 in their Great Prophet 17 drills. The weapon's simple and elegant launcher was also exhibited, comprising of a tilting truck-mounted container holding five UAVs, each catapulted into the air by a small, short-burn rocket engine. In that exercise, the Shaheds were operated in swarms and demonstrated pinpoint accuracy in demolishing stationary tanks, command vehicles and large installations, the most prominent of which was a mock-up of the Israeli nuclear reactor in Dimona.
It subsequently turned out that the Shahed 136 is a 1.5:1 scaled-up (by weight) version of the original, smaller weapon used in the 2019 Saudi attack, now known as the Shahed 131. Apparently, the Iranians increased the size of the original weapon in order to extend its range. The range of the smaller Shahed 131 was estimated as anywhere between 700 and 1,000 km (with 900 km being a common estimate). The range of the 136 version has been estimated by various analysts as anywhere between 1,000 and 2,000 km. There is no available information on the location of its fuel tanks, but if they are in the wings then one way to estimate the range increase is by cubing the ratio between the wingspans of the 136 and 131 versions. The wingspan of the 136 version is 2.5 metres, against the 2.2 metre wingspan of the 131 version – an increase of 13.6%, which when cubed yields an almost 50% increase in the volume of the fuel tanks. If the fuel tanks are located in the fuselage, then its increase in length from 2.6 to 3.5 metres provides a 35% increase in fuel volume. Hence, it stands to reason that the Shahed 136 has a range somewhere between 1,350 and 1,500 km. This fits well with Iran's policy of endowing its long-range weapons with a range sufficient to hit Israel from Iranian bases, which is 1,400 km.
The weapon is frequently dubbed in Western media as the HESA Shahed 136. HESA Aircraft Industries, headquartered in Tehran, was established in Iran during its previous Imperial regime as a Bell Textron factory for licensed production of Bell helicopters. After the revolution it was nationalised and amalgamated into the government-owned Iran Aviation Industries Organisation. Today, HESA provides maintenance services for some of the US-origin Shah-era aircraft still in service. It also manufactures some indigenous aircraft as well as a wide variety of UAVs. The Shahed Aviation Industries Research Centre (SAIRS) is part of Shahed Aviation Industries, located near Isfahan. While HESA has its own design bureau specialising in UAVs, it seems that the powers that be in Iran decreed that SAIRS should function as a design bureau, handing over its designs to HESA for series production – an arrangement which has apparently caused some friction between the two organisations. In any case, this is the origin of the double attribution of the Shahed 131/136 as a ‘HESA Shahed’ product.
The Shahed 136 is ingenious in its simplicity. This, combined with its almost uncanny accuracy, long range and low cost, makes it unique among strategic standoff weapons. Its airframe, made from carbon fibre cloth and honeycomb, can effectively be manufactured by any DIY handyman. Its piston engines are Iranian copies of civilian engines developed for air enthusiasts and the modelmaking market, and as such can be traded free of any export restrictions. The original Shahed 131 is powered by the 38 HP Serat 1 rotary wankel engine, reverse-engineered in Iran from the British AR 731. The larger Shahed 136 is powered by a 50 HP two-stroke, four-piston engine, reverse-engineered from the German-designed Limbach L 550 motor. Both engines are used worldwide by aircraft modelmakers as well as for civilian and military UAVs. The Shahed 136 avionics systems are largely based on commercial-grade products that are traded freely around the world. It navigates using a combination of a commercial-grade inertial navigation system together with GPS and GLONASS satellite navigation systems. It also carries a commercial-grade digital communication device that allows it to receive updates on its target’s location or even change targets. Its warhead is variously estimated to carry 20 to 40 kg of explosives (10 to 20 kg in the case of the smaller Shahed 131).
Many of the components found in the debris of these UAVs in Saudi Arabia and Ukraine are of Western origin. Evidently, the Iranians have managed to exploit the gaps in Western export controls such as the Missile Technology Control Regime – which aimed to block exports of missile- and UAV-related goods and materials – as well as the Wassenar Arrangement controlling the export of dual-use items. Recently, US President Joe Biden established a task force to investigate how 82% of the components found in the Shahed 131 and 136 downed in Ukraine came from the US.
The first unconfirmed news that Russia – mired as it was in its botched Ukraine invasion – intended to purchase Iranian UAVs came in July 2021. This was confirmed in September, when three types of Iranian-designed and produced UAVs were found in Ukraine. One type, the Mohajer 6, is a large reconnaissance/ground attack medium-altitude long-endurance UAV, frequently displayed by Iran in arms exhibitions and military drills (it was also recently supplied to Ethiopia in support of its war against the Tigray insurgents). The two other types were the Shahed 131 and the Shahed 136, fragments of which were first observed in Ukraine in September. As in the case of Yemen, the Iranians were anxious to distance themselves from the Russia–Ukraine conflict, hence they denied supplying them to Russia – although they later modified their position and admitted to selling UAVs to Russia ‘before the outbreak of the war’. The Russians, on their side, repainted the Iranian-supplied UAVs and renamed them Geran (Geranium) 1 and 2 for the Shahed 131 and 136 respectively. Following their first appearance in September, both types joined Russia's ongoing Strategic Operation for the Destruction of Critically Important Targets and were used extensively to hit nodal points in Ukraine's electricity grid and other critical infrastructure in major cities from Odessa in the southeast to Lviv in the far west of the country. Deployed from Belarus and Crimea, their range allows them to hit virtually any point within Ukraine.
By exploiting low-cost commercial and dual-use technologies and components, the Shahed 131/136 has achieved a breakthrough in combining precision with affordability
While a large number of them have been shot down – the Ukrainians claim a success rate of between 50% and 70% in defending against them – they have still inflicted considerable damage, even with their relatively small warheads. President Volodymyr Zelenskyy conceded their effectiveness in his 21 December speech to the US Congress, where he said that ‘Iranian deadly drones, sent to Russia in [their] hundreds, became a threat to our critical infrastructure’.
On 30 November, the spokesman of the Ukraine Armed Forces (AFU) claimed that out of 400 Iranian Shahed UAVs launched to date, 340 (85%) were shot down. He noted a lull in their operations, attributing this to the depletion of the original shipment from Iran; indeed, a three-week hiatus in the use of Shahed 131/136 UAVs in Ukraine occurred between 17 November and 7 December. The reason for this is not clear. One possible explanation is that given by the AFU's spokesperson, namely that the original shipment was totally exhausted by that time, and that operations could be renewed only when a fresh batch of UAVs arrived from Iran. Another explanation is the onset of winter. According to this theory, the Iranian UAVs, designed as they were for Middle Eastern environments, malfunctioned in the freezing temperatures of the Eastern European winter. Ostensibly, the three-week hiatus was needed to ‘winterise’ the weapons.
While the Shahed 131 and 136 are classified as ‘loitering munitions’ by some analysts, they have mainly been used for point-to-point suicide missions rather than as loitering munitions that hunt for opportune targets. ‘Cruise missiles’ are associated in the public’s mind with jet propulsion, while propeller-driven vehicles are considered as ‘UAVs’. This misses the point: any expendable uncrewed aerial vehicle that flies in one direction to hit a predetermined target is a cruise missile, regardless of its propulsion mode. By this definition, the Shahed 131 and 136 deployed in Saudi Arabia and Ukraine are true cruise missiles, albeit of the propeller-driven, slow-flying kind. A loitering version with onboard homing sensors may exist, as is hinted by the successful attacks on moving targets such as the Mercer Street and more recently the Pacific Zirkon (November 2022). Yet if such a version does exist, the Iranians are still keeping it under wraps. In all know instances of their operations to date, whether in Saudi Arabia, Ukraine or against the Kurds in northern Iraq, the Shahed 131 and 136 are configured as cruise missiles.
Defending against the Shahed 131/136 has proved to be frustratingly complicated. The weapons fly low and slow, and once acquired are easy to shoot down, as testified by numerous video clips filmed by Ukrainian bystanders and uploaded to social media. They are being shot down routinely by simple anti-aircraft guns of Second World War vintage, as well as by air-to-air missiles launched from Ukrainian fighter jets. However, their low radar and thermal signatures as well as their low altitudes make them hard to detect from sufficiently large distances. Flying in virtual nap-of-the-earth profiles, they are detected only when close to their targets, providing a very short window of opportunity to engage them. Their only noticeable signature is the lawnmower-like noise from their two-stroke piston engines, which gives the defenders a generalised warning about the direction of their approach. Ukrainian troops in Odessa reported that after succeeding in shooting down several Shahed-type UAVs during the daytime, the Russians switched to night-time attacks. On one occasion, at least, a Ukrainian pilot who shot down a Shahed-type UAV was forced to eject when his aircraft was hit by the UAV's debris.
The Shahed 131/136 epitomises the democratisation of battlefield precision. By exploiting low-cost commercial and dual-use technologies and components, it has achieved a breakthrough in combining precision with affordability. Precision weapons are not new to the battlefield. Three decades ago, in the 1991 Gulf War, precision-guided munitions comprised 8% of the total munitions used by the US-led coalition against Saddam Hussein's Iraq. Long-range, pinpoint-precision cruise missiles have been repeatedly used both by the US and Russia in local engagements, such as US strikes in Afghanistan or Russian strikes in Syria. However, precision has come at a considerable financial cost. For example, the 1,300 kg Tomahawk cruise missile costs the US taxpayer about $2 million at current prices. The 2,200 kg KH 101, a mainstay of Russia's strategic campaign against Ukraine, is reputed to cost six times as much – about $13 million. At such prices, stockpiles have been limited by necessity, forcing Russia to outsource its strategic cruise missiles. The 200 kg Shahed 136 is reputed to cost between $20,000 and $30,000. Its range of about 1,300 to 1,500 km is adequate for theatre operations. It cannot carry nuclear weapons, and its small warhead is about one tenth of that of legacy cruise missiles – but this is compensated by its spectacular precision and even more so by its cheapness, which makes it widely available. No matter how many of them the Ukrainians shoot down, the few that penetrate their defences cause immense damage, and there are always more of them buzzing in for the next attack. Like the broom in the legend of the Sorcerer's Apprentice, the more they are shot down, the more they multiply. Their prevalence, derived as it is from their low cost, makes defending against them an almost Sisyphean labour.
The Shahed 131/136 is a truly revolutionary precision weapon, which challenges the West's defensive technologies and systems. It stands to reason that in time, more effective measures will be found to intercept and destroy them en masse. Western military technologists should strive to achieve this as soon as possible.
This article is part of the Russia Military Report series.
The views expressed in this Commentary are the author’s, and do not represent those of RUSI or any other institution.
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