Iranian-backed Houthi militants, who control swathes of Yemen, have used an array of sophisticated weapons – including ballistic missiles and “kamikaze” drones – in their attacks on international shipping in the Red Sea in support of Palestinian militant group Hamas in its war with Israel in the Gaza Strip.

The attacks began on Nov. 19 when Houthi commandos landed a helicopter on the Galaxy Leader cargo vessel as it was passing through the southern Red Sea. They redirected it toward Hodeidah port in Yemen and seized the crew, who are still being held.

Since then, 29 more ships have been attacked in the area, with 13 of those suffering direct strikes from missiles or drones. The attacks have caused major disruptions to global trade, some 12% of which passes through the Red Sea.

Reuters has cataloged the ships attacked so far and examined how Houthi militants are using a combination of weapons to target commercial ships. The analysis shows how Houthi drone and missile activity has escalated since the Gaza war began, and has continued despite Western military airstrikes on their bases in Yemen, which began on Jan. 11.

Houthi attacks have targeted ships in the southern Red Sea and the neighboring Gulf of Aden, which are joined by the Bab al-Mandab strait, a chokepoint between the Horn of Africa and the Middle East.

In Arabic, Bab al-Mandab means “Gate of Tears”, a reference to the strait’s precarious navigation. The narrow waterway lies between Djibouti and Eritrea on the coast of east Africa and western Yemen, much of which is under Houthi control.

Bab al-Mandab is a strategic link between the Mediterranean Sea and Indian Ocean: exports to the Western markets from the Gulf and Asia must pass through before entering the Suez Canal.

At only 18 miles wide at its narrowest point, shipping traffic is limited to two channels for inbound and outbound shipments, leading to occasional congestion.

The Houthis, who control the most populous regions of Yemen, say they will continue their attacks until Israel halts its “siege” of Gaza. The Israeli government has pledged to continue its offensive in Gaza until it has secured the release of hostages seized in the Oct. 7 attack on Israel by Hamas and destroyed the Palestinian militant group.

A Reuters analysis of reported incidents shows how Houthi drone and missile strikes have escalated since the Gaza conflict erupted, and have continued since Western airstrikes began against land targets inside Yemen on Jan. 11. In the past week, the pace of those airstrikes has slowed, while interceptions of missiles and drones by U.S. and allied naval forces in the area has increased.

Fabian Hinz, open source analyst and research fellow at the International Institute for Strategic Studies (IISS), a military think-tank based in London, said it was unclear how far Western airstrikes had depleted the Houthis’ capabilities. “I would say in general it’s almost impossible to degrade an arsenal like that 100%,” he said.

The Houthis have said the airstrikes have had no effect on their capabilities. A spokesman for the group did not respond to requests for comment for this story.

Many of the Houthi attacks have been on container vessels and dry bulk carriers. However, on Jan. 26, the Marlin Luanda oil tanker – operated on behalf of international commodity trader Trafigura – was hit by a Houthi anti-ship missile in the Gulf of Aden, causing a fire that lasted several hours.

While no casualties were reported, the incident was the most destructive of the crisis so far, shipping and insurance sources said.

“The recent strike on the Marlin Luanda highlights the ongoing risk to vessels and the likelihood that the current crisis will impact shipping and commodity markets for the foreseeable future,” data and analytics group Kpler said in a Jan 30 report.

The Houthi arsenal

In a show of strength in September, the Houthis paraded thousands of troops and trucks carrying weaponry in the capital Sanaa, including cruise and ballistic missiles as well as long-range armed drones. Armored vehicles and speed boats displayed signs that read: “Death to America, death to Israel!”

The Houthis, who emerged in the 1990s as an armed group in opposition to Saudi Arabia’s religious influence in Yemen, have long received funds, arms and training from Iran, according to regional and military experts.

Despite voicing support for the Houthi campaign, Iran has denied it provides the Yemeni group with weapons and intelligence. The Houthis have insisted they manufacture their own weapons and do not receive arms or take orders from Iran, even if they maintain a close relationship.

September’s military parade showcased Iranian-made weapons, including a surface-to-surface Iranian Toofan missile, which has a range of 850 to 1,200 miles (1,350-1,950 km), making it capable of reaching Israeli territory, according to a report from the Meir Amit Intelligence and Terrorism Information Center (ITIC), an Israel-based think-tank that researches Islamist groups and militias.

The parade also featured new shore-to-sea missiles capable of hitting vessels in the Red Sea, among them Tankil missiles, which have an estimated range of about 300 miles (500 km), and Quds Z-0s, which are cruise missiles capable of hitting targets both on land and at sea, ITIC said.

When the Houthis seized Sanaa in 2014, ousting the Saudi-backed government, they also inherited military equipment and staff with know-how from the previous government, notably short-range ballistic missiles as well as surface-to-surface and cruise missiles, some deployed on patrol craft, according to a specialist with Universal Defence and Security Solutions, a UK-based consultancy.

Their new Iranian-made weapons include Qasef-1 and Qasef-2K reconnaissance and attack drones, said the specialist, who declined to be named due to the sensitivity of the issue. While cheap and basic, these drones have a 50-60 mile range with a small warhead of around 30-40 kgs.

Other drones included the Sammad 1, 2 and 3, which are similar to the Qasef with a longer range of around 300 miles and smaller 18 kg warheads, he said.

The defence specialist said that supplies of weapons systems and parts from Iran meant the Houthis should be able to sustain the near-daily rate of attacks in the Red Sea. In addition, the Houthis were able to produce some of their own munitions for basic rockets and drones, he said.

“It’s not particularly important that many of the fired weapon systems do not cause any significant damage: the disruptive impact on maritime trade, which relies on insurance, is quite easy to maintain, causing significant financial impact and operational complexity,” he said.

The Pentagon and the British Department of Defence did not immediately respond to requests for comment.

One-way attack drones

Western military and shipping companies have shared little information publicly on the types of drones used in recent Red Sea shipping attacks.

On Nov. 29, U.S. Central Command (CENTCOM) – which covers the Middle East, Central and South Asia – said that the destroyer USS Carney shot down an Iranian-produced KAS-04 drone – the U.S. designation for the Samad drone – launched from Houthi-controlled areas of Yemen.

A report commissioned by the Oil Companies International Marine Forum (OCIMF), an association of petroleum firms focused on promoting safer and cleaner shipping, identified the Shahed-136 as the “loitering munition” most commonly used against merchant ships operating in the Middle East. These types of drones can circle in an area before a final target is determined.

The Shahed was employed for the first time by the Houthis in Yemen’s war between September and December 2020, according to the report, published in August and produced by global risk analysts Sibylline.

The Shahed-136 – which has been extensively used by Russian forces in Ukraine – can be fired from truck-mounted containers at a slightly upward angle. A small rocket booster helps propel the drone into the air before being jettisoned. Its main piston engine then takes over to power the flight.

The drone will travel towards coordinates it has been assigned. Loitering munitions usually have a navigation system to calculate their speed and position, and sometimes possess sensors connected to commercial satellite networks.

Images released in November 2022 of a Shahed-136 used to attack the MV Pacific Zircon off the coast of Oman indicated a satellite receiver on board, which could enable real-time navigation, according to the OCIMF paper. This technology might also allow Houthi operators to manually alter target coordinates in-flight.

Once the drone has passed any obstacles and cleared the coast it can take a lower flight path to try to avoid radar. The delta-wing design of the Shahed-136 gives it a low radar signature. Combined with its ability to travel at low-altitude, this makes detection by commercial radar difficult.

As the noisy drone approaches target areas, the distinctive sound of its small piston engine can be heard, resembling the noise of a moped. They are also relatively slow.

Taimur Khan, regional head of operations in the Gulf for Conflict Armament Research, an investigative organization that tracks weapons used in conflicts, said Houthi drones documented during the civil war were designed to hit static targets by using GPS coordinates. But the shipping attacks appeared more sophisticated.

“In order to reliably hit a moving target such as a cargo ship, even a relatively slow-moving one, there would need to be some kind of terminal guidance,” he said.

Once a target has been acquired, loitering munitions can adjust trajectory, and attack from the top-down, detonating upon impact.

Lebanese Shia group Hezbollah – another member of Iran’s ‘Axis of Resistance’ in the Middle East – has provided military training and assistance to the Houthis, military and regional experts say.

The Houthis have denied this. Hezbollah has not commented.

Eyal Pinko, a former senior official with Israel’s intelligence services until 2017 who now works at Bar Ilan University’s Begin-Sadat Center for Strategic Studies, said Hezbollah had in particular helped the Houthis to build their naval capabilities.

These include seven naval bases and 30 control posts along Yemen’s coast that have radar and electro-optical directors for better control of missile launches, said Pinko, who has studied the Houthis since 2004.

“It’s a massive coastal defense line for detection, and they’re also using AIS (ship tracking) systems, and also intelligence from Iran,” Pinko said. Automatic identification system, or AIS, is a transponder system that allows maritime authorities and companies to publicly track commercial shipping and identify vessels.

Among the unused weapons in the Houthis arsenal are Iranian-made Sadaf floating mines. While such munitions are relatively unsophisticated and easy to deploy, their impact on merchant shipping would be considerable if they were used in the Red Sea, said Pinko, who also consults on private-sector security.

Floating mines have been placed with great effect in the Black Sea during the war in Ukraine, sowing alarm amongst shipping companies and their insurers.

Pinpoint strikes

The United States, Britain, and other allied nations, have carried out strikes from the air and sea against Houthi military targets in Yemen in response to the attacks on shipping.

The first wave of strikes were conducted on Jan. 11: overnight attacks by the U.S. and Britain targeting almost 30 different locations in Yemen. Strikes continued throughout January.
The Pentagon says it has struck anti-ship missiles on the ground, as well as coastal radar and Houthi air surveillance capabilities and weapon storage sites.

Satellite images taken by Maxar Technologies the day after the Jan.11 strikes show the aftermath. In a compound on the Yemeni coast, bordering the southern Red Sea, craters and scorched earth can be seen. A similar image from Google Earth, taken by Airbus, shows structures in the same location in July last year.

One kilometer north along the coast, a similar compound was struck during the same wave of attacks on Jan.11. Images from Maxar Technologies show scattered debris and structures missing, when compared to a July 2 Airbus image.

Maxar also published images of locations on the outskirts of Sanaa airport showing what appears to be damage when compared to older images. One was described by Maxar as a radar facility, while the other location was unspecified.

Reuters was unable independently to determine the use of the sites or whether they were hit by Western missiles. However, both appear to have been targeted with accuracy.

CENTCOM has said U.S. strikes have hit a number of Houthi anti-ship missiles that were about to be launched.

“This is quite difficult from an intelligence and targeting perspective because you need to know where the missile is, where it’s moving, where they want to fire it from,” said Hinz, the IISS research fellow.

“That indicates that the Americans are having some success,” he added. “We still don’t know to what degree they’ve degraded the (Houthi) arsenal.”

Global Shipping Disruptions

Shipping companies have been re-routing some sailings via Africa’s southern Cape of Good Hope as the attacks continued. The disruption threatens to drive up delivery costs for goods, raising fears it could stoke global inflation.
Container shipping, which transports consumer goods, has been the segment most impacted by the attacks in the Red Sea due to fixed routes through the waterway.
In the period from the start of December last year to Jan. 30, 373 container ships are estimated to have re-routed around Africa, according to analysis from supply chain platform project44.
The number of container vessels sailing through the Suez Canal has fallen by about 65% since the attacks began, project44 data showed.

Because of the high risks, seafarers are signing agreements to receive double pay when entering the high-risk zones around Yemen, according to contract agreements viewed by Reuters and union officials.

“There is a fair degree of trepidation from the seafarers because quite a few ships are being hit,” said Stephen Cotton, General Secretary of the International Transport Workers’ Federation, the leading union for seafarers.

“The feedback from the captains is, certainly on the container trades, they’re much happier to go around the Cape.”

The Suez Canal is used by roughly one third of global container ship cargo. Redirecting ships around the southern tip of Africa is expected to cost up to $1 million in extra in fuel for every round trip between Asia and northern Europe.

Worries about potential disruption to Middle Eastern supply after the latest Red Sea attack drove oil prices higher in the first trading session of 2024.