Six Houthi drone warfare strategies: How innovation is shifting the regional balance of power

On 19 July 2024, a Houthi drone flew for some 16 hours from Yemen over a distance of more than 2,600 kilometers to reach Tel Aviv, where it killed one Israeli citizen and injured at least eight others. Although Houthi forces had been launching drones and missiles at Israel since October 2023, this was the first time a Houthi drone made it past Israeli air defenses, let alone resulted in casualties on Israeli soil.¹On 17 March 2024, a Houthi cruise missile flew past Israeli air defenses but landed in an open area north of Eilat without causing any damage or casualties. As perhaps one of the most emblematic Houthi drone attacks to date, it highlighted the group’s increasing ability to leverage drone technology. 

Drone warfare is becoming a prominent feature in modern military strategies and conflicts, with the proliferation of drones rapidly increasing across multiple conflicts. Whereas only three countries possessed armed drones in 2010,²Michael Horowitz, Joshua A Schwartz, and Matthew Fuhrmann, ‘Who’s prone to drone? A global time-series analysis of armed uninhabited aerial vehicle proliferation,’ Conflict Management and Peace Science, March 2022 by 2024 that number had expanded to over 40 countries.³Drone Wars, ‘Which countries have armed drones?,’ February 2024 In addition, one-way attacks and commercial off-the-shelf drones, used by both state and non-state actors, have significantly increased drone activity, with ACLED recording drone usage in conflict in at least 34 countries in 2023. Drones can have a decisive impact in war scenarios, with Houthi drone warfare strategies providing a compelling case study to answer the following question: has drone technology altered the balance of power between the warring parties in the Yemen conflict?

The Houthis, although relatively new to drone technology, have been at the forefront of drone warfare. They established large-scale drone production around 2018, leveraging Iranian technology transfers,⁴Conflict Armament Research, ‘Iranian Technology Transfers to Yemen,’ March 2017; Conflict Armament Research, ‘Evolution of UAVs employed by Houthi forces in Yemen,’ February 2020 and achieved remarkable military successes, such as compelling Saudi Arabia and the United Arab Emirates to accept a ceasefire in April 2022. More recently, they have been enforcing a partial blockade on maritime traffic through the Red Sea since November 2023. A thorough analysis of the main strategies employed by the Houthis illustrates how drone technology can provide a tactical advantage, exploiting the structural weaknesses of the enemy in creative ways to achieve symbolic victories. However, for these tactics to remain effective, continuous innovation is essential. Following a brief introduction to the general trends of Houthi drone warfare, this report outlines six key strategies employed by the group in Yemen and beyond its boundaries.

Houthi drones in the Yemen war

Since the first recorded attack in September 2016, Houthi forces have used armed drones, also known as unmanned aerial vehicles (UAVs), in over 1,000 distinct events, which were directly responsible for more than 700 reported fatalities. Across both 2016 and 2017, however, Houthi forces’ use of armed drones remained limited, with only 10 attacks recorded over the two years, all in Yemen. The attacks were carried out with the Qasif-1 suicide drone (see table below), likely imported from Iran, where it is known as the Ababil-T drone. Houthi forces did not officially claim the attacks, as they were most likely testing out the new technology.

*Houthi drone activity between January 2015 – June 2024
**This does not include 136 reported events of reconnaissance drone activity

Houthi forces revealed the existence of a drone program in February 2017 and claimed the first attack from their ‘air force’ in April 2018. In 2019, they unveiled three new suicide drones: the Sammad-2, the Sammad-3, and the Qasif-2K.⁵Houthi forces also unveiled the Sammad-1 drone, which was presented as a reconnaissance drone, but that can also be weaponized as a suicide drone. While the Qasif-2K was presented as an improved version of the Qasif-1, the Sammad drones were more advanced drones designed to penetrate deep inside Saudi territory.⁶The maximum range of the Sammad-3 is estimated to be around 1,500 kilometers, against 200 km for the Qasif-2K. 

Houthi drone attacks increased from 2018 to 2019, with a shifting focus from Yemen to Saudi Arabia, and remained stable from 2019 to 2020 (see graph below). ACLED records an all-time high of Houthi drone attacks in 2021, a year notable for the group’s introduction of new commercial-grade drones that drop small explosives on targets rather than crashing into them. Among these was the Rujum multi-use drone, which the Houthis unveiled in March 2021.⁷Ansar Allah, ‘Specifications of the ‘Rujum’ drone,’ 11 March 2021

The implementation of the United Nations-mediated truce in April 2022 halted Houthi drone attacks on Saudi Arabia and the UAE. However, Houthi drone attacks in Yemen increased to reach an all-time high. Frontlines froze as a result of the truce, prompting warring parties to shift to remote forms of violence instead of direct confrontations, a trend that continues to this day. Houthi forces resumed the large-scale use of suicide drones beyond the borders of Yemen in November 2023. As a response to the Israel-Gaza conflict, the group has sought to impose a blockade of Israel by targeting commercial shipping in the Red Sea and surrounding waterways, as well as carrying out attacks directly targeting Israeli territory. Since November 2023, more than 50% of all Houthi drone attacks have been launched toward targets outside of Yemen.

1. The deployment of drones to support domestic ground offensives

The Houthis have leveraged drone technology in a few key military campaigns, aiming to upset the power balance on the ground. For instance, between April and June 2018, drones played a key role in the attempt to thwart the UAE-backed offensive on the West Coast by degrading their capabilities. The first-ever drone attack claimed by Houthi forces inside Yemen targeted UAE command centers and Patriot systems in al-Hudayda and Taizz governorates in April 2018. ACLED records more than 60% of all Houthi drone attacks in Yemen that year in these two governorates (see graph below). Although Houthi officers publicly claimed that the Qasif drone changed the equation in their confrontation with UAE-backed forces,⁸Yemen News Agency (SABA), ‘Military media distributes photographs, scenes of Yemen Drone Force in West Coast,’ 3 July 2018 the group eventually agreed to a ceasefire after the siege of al-Hudayda city.

In 2021, another Houthi military campaign in northern Marib featured extensive drone deployment. The renewed offensive to capture Marib city – after a first failed attempt in 2015 – saw the Houthis heavily rely on drones, with ACLED documenting 50% of all Houthi drone attacks that year in this governorate (see graph above). Notably, this campaign marked the deployment of multi-use drones in the Houthi arsenal. It involved using Qasif drones to target positions of the Internationally Recognized Government (IRG) from a distance, including inside Marib city, alongside multi-use drones employed for close-range frontline engagements. However, despite committing extensive resources, the Houthis ultimately failed to capture Marib city.

The campaigns on the West Coast and in Marib were crucial for the Houthis. Yet, despite the substantial use of drones, they did not achieve military superiority on the battlefield. Critically, an overall analysis of Houthi drone attacks suggests that the group does not automatically deploy drones in every military campaign. For instance, ACLED records very few Houthi drone attacks in the northern governorate of al-Jawf in both 2020 and 2021, and only one Houthi drone attack in al-Dali governorate in 2019, despite intense fighting between Houthi and anti-Houthi forces. Although it is unclear what exactly drives the group to use drones in support of ground offensives, the Houthis are likely prioritizing this strategic resource for military campaigns they deem of higher importance or where success is more uncertain. 

2. Cross-border drone strikes on critical infrastructure to put pressure on regional powers

Between 2018 and 2022, the Houthis used drone technology as part of asymmetric warfare tactics targeting critical infrastructure in Saudi Arabia and the UAE. This strategy aimed to highlight the vulnerability of both countries by attacking civilian airports and hydrocarbon facilities rather than pursuing frontline military dominance. From 2018 to March 2022, before the implementation of the UN-mediated truce in April 2022, 43% of all Houthi attacks on Saudi Arabia targeted civilian airports and energy infrastructure. By exploiting Riyadh’s and Abu Dhabi’s low tolerance for risk and insecurity, the Houthis gained a mid-term strategic advantage, ultimately influencing them to accept a ceasefire.

Cross-border drone warfare started to escalate in July 2018, with highly symbolic extended-range drone attacks targeting a Saudi Aramco oil facility on 22 July and Abu Dhabi International Airport on 26 July. In 2019, Houthi drone operations against Saudi Arabia increased by more than seven times compared to the year prior, with nearly half the attacks targeting civilian airports (see graph below). Most attacks made use of the short-range Qasif-2K drone, with the Houthis justifying their targeting of civilian infrastructure as retaliation in response to the Saudi-led Coalition’s “siege of Sanaa airport.”⁹X @abdusalamsalah, 9 June 2019 The strategy proved effective, with interception rates staying extremely low and over half of the strikes resulting in hits in 2021.

Contrastingly, the attacks on Saudi hydrocarbon infrastructure used long-range Sammad drones, which are more difficult to manufacture, likely leading the Houthis to use them less frequently (see graph above). These weapons were highly effective, with just 20% of drone attacks on Saudi hydrocarbon infrastructure intercepted between 2018 and 2022. A prominent example is the joint Houthi-Iranian attack that targeted Saudi Aramco facilities in Abqaiq and Khurays on 14 September 2019. The incident temporarily knocked out more than half of Saudi Arabia’s oil output and nearly 5% of the global oil supply.¹⁰Al Jazeera, ‘Saudi oil attack: All the latest updates,’ 30 September 2019 

The operation highlighted several advantages of asymmetric drone warfare: vulnerability of Saudi air defense systems to drone attacks, as radar cannot always detect devices flying at low altitude, and due to the use of swarm attacks; lack of accountability, due to near anonymous strikes, and consequent plausible deniability for the assailants; and financial asymmetry, with low-cost drone devices outmatching high-cost air defense systems.

3. The development of multi-use drones for cost-effective violence on the frontlines

The introduction of multi-use drones in 2021 was a turning point in the development of Houthi drone technology, with immediate effect on the battlefield (see map below). Unlike single-use drones designed to crash and explode on impact or just above ground, these multi-use drones drop explosives on targets and return to base for reuse in similar missions, making them more cost-effective.

The Houthis officially unveiled the Sammad-4 and the Rujum multi-use drones in March 2021. While ACLED has never recorded the use of the Sammad-4, the data show that the Rujum, an adaptation of a Chinese civilian hexacopter drone, has been used in more than 25% of Houthi multi-use drone attacks since March 2021.¹¹The Rujum can carry a payload of up to 18 kilograms. It was initially displayed with six 60 millimeter mortar rounds, but it has since appeared with smaller munitions, and has also been reported to carry larger 120 mm mortar rounds. Houthi forces have also been attaching small explosives to civilian drones from the Mavic and Matrice series made by Chinese company DJI.¹²X @VleckieHond, 1 May 2021

Commercial-grade drones used as multi-use devices are both cheaper and easier to obtain than military-grade suicide drones. Their addition to the Houthi arsenal led to a 50% increase in Houthi drone attacks in Yemen from 2020 to 2021, with the overall number of attacks in 2021 alone surpassing the total number of attacks from 2018 to 2020. This upward trend continued into 2022. Low-cost multi-use drones like the Rujum, with operating ranges between 10 and 30 kilometers, are used for direct frontline activity. Since the implementation of the UN-mediated truce in April 2022 and the subsequent freezing of frontlines, Houthi forces have employed multi-use drones to attack enemy forces, replacing direct ground confrontations.

New low-cost drones have also gradually replaced larger suicide drones on domestic frontlines. Since March 2021, the use of suicide drones inside Yemen has been prevalent only during the Houthi offensive on Marib in 2021 and the Houthi counter-offensive in Hajjah governorate in early 2022. With the exception of these two instances, suicide drones have been kept for more strategic strikes deep into IRG territory since 2021. 

4. Combined drone-missile attacks to strike behind the frontlines

Since the beginning of the conflict in 2015, the Houthis have used rocket and missile attacks to target enemy military camps behind the frontlines, exploiting the element of surprise. Despite numerous attacks, this strategy has resulted in just a few reported fatalities, mainly from incidents involving ballistic missiles from the stockpiles of former President Ali Abdullah Saleh, which the Houthis depleted in late 2016 or early 2017. Since 2018, though, drone technology has revitalized this military strategy, enhancing its effectiveness and lethality. 

A salient example of this strategy is the attack on al-Anad airbase in Lahij on 10 January 2019. The Houthis deployed a new, modified version of the Qasif-2K drone, which exploded over a military parade, raining shrapnel over IRG officials. The attack reportedly resulted in eight fatalities, including the head of the IRG intelligence, and 20 injuries. This incident had a strong symbolic impact because of the new technology deployed and the fact that it targeted IRG officials away from the frontlines.¹³X @ERYANIM, 10 January 2019

In a further development, between 2019 and 2021, the Houthis conducted targeted attacks on military camps using a combination of drone and missile technology, resulting in three times higher lethality compared to drone attacks alone (see graph below). On 1 August 2019, for instance, the group targeted a military parade in a Security Belt Forces camp in Aden city with a Qasif-2K drone and a ballistic missile, killing at least 36, including senior commander Abu al-Yamama. Following the incident, infighting erupted within the IRG ranks.

The unprecedented modality of these attacks caught the IRG off guard, allowing the Houthis to target high-profile officers. Furthermore, the timing of the attacks and the specific political context in which they occurred helped amplify their symbolic relevance.¹⁴On several occasions, Houthi forces have refrained from claiming high-profile attacks beyond the frontlines. Whether intentional or not, this has often sowed discord within the anti-Houthi camp. In 2021, the Southern Transitional Council noted to the UN Panel of Experts that when Houthi forces carry out attacks without claiming them, “they allow for speculation as to who may be responsible, and create further distrust among anti-Houthi forces.” See: United Nations Security Council, ‘Letter dated 25 January 2022 from the Panel of Experts on Yemen addressed to the President of the Security Council,’ 25 January 2022 

5. Drone attacks to curb IRG revenues

In 2022, drone technology enabled the Houthis to wage a new form of economic warfare with several attacks on targets associated with the Yemeni oil industry, forcing an end to IRG oil exports. The decision to engage in this tactic coincided with the failure of negotiations around the disbursement of IRG oil revenue. The Houthi leadership demanded the disbursement of salaries for all public employees in areas under their control using oil and gas export revenues in exchange for a renewal of the UN-mediated truce that was coming to an end in October. The US special envoy to Yemen at the time described the Houthis’ economic demands as “maximalist,” and the truce ultimately collapsed.¹⁵Asharq Al-Awasat, ‘US Envoy: Houthis’ ‘Maximalist and Impossible Demands’ Failed UN Truce,’ 6 October 2022

In response, the Houthis decided to restrict the IRG’s sources of financial revenue. After issuing several warnings to domestic and foreign companies, they decreed a ban on hydrocarbon exports and enforced the decision by launching a string of drone attacks on oil tankers and infrastructure in the southern Yemeni provinces of Shabwa and Hadramawt in October and November 2022 (see map below). Despite their limited number and the negligible damage they caused, the attacks successfully halted the IRG’s hydrocarbon exports, causing an estimated loss of more than 1 billion US dollars in 10 months.¹⁶Yemen Future, ‘Washington: An international report says that the Yemeni government’s losses due to the cessation of oil exports exceed one billion dollars in ten months,’ 8 October 2023

What is peculiar about this case is the timing of Houthi drone operations. The same drone technology had been available to the group for years. Yet, the Houthis had considered targeting Yemen’s domestic oil infrastructure to be a ‘red line’ because it carried reputational risks. Moreover, prior to 2021, the value of oil production was negligible, making the trade-off between economic disruption and reputational costs less advantageous for the Houthis.¹⁷Al Araby, ‘The Yemen war… What are the goals of the Houthi group in targeting the port of Dabbah?,’ 22 November 2022 Indeed, the attacks resulted in unanimous international condemnations and led the IRG to designate the Houthis as a terrorist group, putting further strain on negotiations to renew the truce.¹⁸Sana’a Center for Strategic Studies, ‘Houthi Strikes Prompt Government Terrorism Designation,’ 14 November 2022 Moreover, they marked a precursor to the ongoing Red Sea crisis and signaled a shift in Houthi politics, highlighting their growing disinterest in achieving legitimacy in the eyes of the international community.

6. Maritime drone attacks to impose a blockade in the Red Sea 

Since the outbreak of the Israel-Gaza conflict following the 7 October 2023 attacks, the Houthis have shifted their military focus to the Red Sea, aiming to enforce an embargo on Israel and halt Tel Aviv’s offensive on Gaza. In a continuous escalation, the Houthis initially targeted Israeli territory before subsequently expanding their objectives to vessels linked to or en route to Israel, as well as to US and UK warships and interests, continuously extending their pool of targets and effectively disrupting global trade transiting through the Red Sea.¹⁹Yeni Safak, ‘Egypt says Suez Canal revenue falls 50% amid Red Sea tension,’ 28 April 2024; Maersk, ‘Maersk Q1 results in line with expectations amid ongoing Red Sea disruptions,’ 2 May 2024

Houthi operations targeting international shipping in the Red Sea and surrounding waterways have significantly relied on drones, with more than 40% of the events ACLED records between October 2023 and June 2024 involving drones. However, the effectiveness of drone attacks to target international shipping has been considerably limited if compared to missile attacks. In fact, 75% of Houthi drone attacks on international shipping have been intercepted by international coalition forces deployed to the Red Sea and the Gulf of Aden region to counter the Houthi threat, compared to approximately 16% of missile attacks.²⁰Of the 85% of Houthi missile attacks that were not intercepted by international forces, 26% struck their target, while the rest impacted the water without causing any damage. Furthermore, among attacks that successfully hit the target, drones were used in only one out of five cases.

Indeed, the drones’ chance of hitting the target is secondary to Houthi tactics. The group can manufacture these devices in large quantities and at low cost, and drones are used primarily to raise threats to navigation without causing direct damage to vessels. This strategy minimizes the Houthis’ reputational backlash and compels the international coalition to deploy costly air defense systems against comparatively inexpensive devices. 

Furthermore, the Houthis appear to deploy different weapon types based on the target’s geographical location. Drones are primarily used to target objectives in the southern Red Sea, which is closer to Houthi-controlled areas, while missiles are mainly used in the Gulf of Aden (see map below). A possible explanation is that, given that drones are slower devices than missiles, the Houthis use them in the smaller area of the southern Red Sea to avoid an even higher interception rate in the Gulf of Aden region, where international forces would have more time to react.

How the Houthis can sustain drone warfare

The Houthis gained reliable access to drone technology in 2018 and have since acquired increasingly advanced devices. As proven by the six strategies outlined above, Houthi drone warfare strategies have significantly impacted the trajectory of the Yemen conflict. Houthi drone attacks have proven extremely effective in securing symbolic victories through targeted strikes, either by destabilizing the IRG faction or by exposing the vulnerabilities of regional and international powers. However, drones have been far less effective in ground battles, failing to achieve strategic goals or shift the military balance in favor of the Houthis.

Drone technology and its rapid evolution have granted the Houthis a short- to mid-term tactical advantage, allowing them to consistently stay one step ahead of the enemy. The group has been able to identify and exploit the enemy’s weaknesses, delivering successful attacks through continuous technological innovation, expansion of military targets, and the low propensity of its adversaries to accept war-related risks on their territory and close to their financial interests.

This analysis raises the question of how long Houthi drone attacks will maintain their effectiveness and success. The answer involves two variables. First is the Houthi’s capacity to innovate: how long will they be able to identify new targets and develop new strategies? Arguably, the pace of innovation is likely to slow down in the near future unless new red lines are crossed by the group, as recently threatened by Houthi spokesperson Muhammad Absdussalam.²¹Kersten Knipp, ‘Violence between Houthi rebels and Israel escalates,’ DW, 22 July 2024 However, small technological advancements – such as the engine that increased the range of the Sammad-3,²²X @fab_hinz, 19 July 2024 enabling the 19 July attack on Tel Aviv – continue to offer potential for new targets and strategies. In this regard, the role of Tehran in providing training, components, and cutting-edge technology will remain key to Houthi military success.

A second variable is the capacity of the anti-Houthi camp to adapt to Houthi strategies while bridging the gap created by asymmetric warfare. Saudi Arabia has already procured new air defense systems, and more are on the way,²³Paul Iddon, ‘Saudi Arabia Diversifying Air Defenses And Boosting Local Industries,’ Forbes, 14 May 2024 but it is unlikely that it will completely neutralize the drone threat. Meanwhile, Operation Prosperity Guardian is grappling with the cost of downing inexpensive drones with expensive missiles. Overall, the greatest challenge, both for regional and international powers, remains accepting the fact that risks associated with asymmetric warfare will remain largely unavoidable.

Lastly, the Houthis’ newly acquired regional reputation, combined with the strategic location of their strongholds, also increases the risk of them becoming direct or indirect vectors for drone proliferation. Drone attacks by Al-Qaeda in the Arabian Peninsula in southern Yemen since May 2023 seem to have been facilitated by Houthi training and logistical support. In addition, the Houthis appear to be involved in weapon smuggling to the Horn of Africa. The group’s actions in the Red Sea clearly demonstrate a successful strategy that insurgent groups and non-state actors might adopt to challenge the military dominance of state and international forces in the region.