Red Sea crisis expanding as the fourth phase of Houthi maritime operations comes to a close

Since the start of the Houthis’ Red Sea attacks on 19 October, the group has targeted nearly 80 ships in the Red Sea and Gulf of Aden with missiles and drones, disrupting global trade and prompting a US-led military intervention. A US naval commander described the maritime hostilities as the “most significant … in two generations” since the so-called Tanker War of the 1980s.¹Jon Gambrell, ‘Iran is ‘directly involved’ in Yemen Houthi rebel ship attacks, US Navy’s Mideast chief tells AP,’ Associated Press, 22 January 2024 The conflict, though, has not remained static, instead evolving through a series of step-changes marked by shifts in the location, targeting, operational tempo, and tactics of the Houthi forces.

To date, the Houthis have launched 164 missiles and 265 drones at 79 ships, hitting 29 merchant vessels and sinking one of them, as well as killing three seamen (see graphic below). Over the past six months, the Houthi maritime operations have evolved through four phases. Each of these phases has been delineated by changing patterns in the location and targets of the Houthi attacks, spreading from Israel to the Red Sea and the Gulf of Aden and now into the Indian Ocean while the targeted ships has expanded from initially just Israeli vessels to all ships with slight connections to Israel, the US, and the UK. 

Also the timing of the shifts has become increasingly more influenced by broader regional and international developments as the conflict has progressed. The direct military engagement of US forces has been a factor in the start of the fourth phase and intensifying Israeli-Iranian tensions have influenced the tempo of Houthi attacks throughout the past four months. As the conflict passed the seven-month point, the Red Sea crisis appeared primed to evolve once again, bringing an end to the prolonged fourth phase of the Houthi attacks and opening a fifth stage in the group’s maritime activities. 

Fourth phase marked by a shift to the Gulf of Aden and the targeting of US and UK ships

The Red Sea attacks began on 19 October, triggered by the start of the Israeli military campaign in Gaza and, at first, primarily consisting of unsuccessful long-range missile and drone launches toward southern Israel (see graph below). This was followed by a move in November to targeting Israeli-linked vessels closer to Yemen, mainly in the southern Red Sea. From December, the Houthis declared all vessels heading to Israel to be legitimate military targets and started operations in the Bab al-Mandab.

The start of the fourth phase was marked on 9 January by the Houthis claiming their first attack on a US warship, followed by the first round of US-led strikes on Houthi military assets in Yemen. Over the next three months, 16 of the ships attacked had ties to US- and UK-based owners and operators compared to only three before the start of the year. Among these attacks were several of the most notable incidents, including the sinking of the British-owned Rubymar cargo ship, the first and only vessel sunk in the Houthi attacks so far, in the south of the Red Sea.

The group also expanded its operations to the Gulf of Aden, where over a third of the 132 attacks have been recorded since January, compared to only one incident in the Gulf in the three previous phases. Among the attacks waged on ships navigating in the Gulf of Aden were the only reported fatalities since the start of the Red Sea escalation: on 6 March, a Houthi missile strike on the True Confidence, a Barbadian-flagged, Liberian-owned bulk carrier, reportedly killed two Filipino crew members and a Vietnamese seaman and injured at least four more sailors. 

Houthi maritime attacks increasingly tied to regional rather than domestic developments 

Overall, the tempo of the Houthi military actions fluctuated significantly during the prolonged fourth phase, which was marked by two distinct parts. January and February were the most active months of Houthi maritime attacks to date, peaking in the second half of February with 27 incidents, almost as many as during the first two phases combined.

In mid-February, several regional and international developments seemingly conspired to influence the surge in Houthi attacks. Houthi officials, including the group’s leader Abdulmalik al-Houthi, made repeated threats to escalate the group’s maritime activities if Israel launched an assault on Rafah.²Saba Net, ‘The Leader of the Revolution confirms that the enemies failed to achieve their goal of targeting President Saleh Al-Samad,’ 13 February 2024 The US designation of the Houthis as a Specially Designated Global Terrorist (SDGT) group also came into effect on 17 February, to which the Houthis had previously threatened a response if implemented.³Matt Murphy, ‘Yemen strikes: Houthis hit US-owned ship after ‘terror’ designation,’ BBC, 17 January 2024 Mirroring the accelerated Houthi attacks, the US-led strikes also hit their peak in February, including two of the heaviest rounds of pre-planned, degrading strikes to date.⁴Dan Lamothe, ‘U.S., Britain launch new wave of strikes against Houthis in Yemen,’ The Washington Post, 24 February 2024

The adjustment in the group’s focus to the Gulf of Aden was accompanied by a drop-off in the Houthi attacks toward Israel (categorized as the North Red Sea in the map above). Attacks toward Israel had been dwindling since November as the group’s resources were directed away from the unsuccessful long-range launches to more achievable, closer-to-home targets. The Houthis’ stores of the weaponry required for long-range launches may have been diminished by the US-led strikes, depleted missile reserves, and the deployment of US and European Union naval missions to the Red Sea.⁵Michael Knights, ‘Assessing the Houthi War Effort Since October 2023,’ CTC Sentinel, pp. 11-15, April 2024

However, the group retained the capacity to attack Israel, and the launches resumed intermittently from 2 February, frequently coinciding with intensified activity by aspects of the Iran-led ‘axis of resistance’⁶Al-Arabiya, ‘Houthis launch drones at Israel as Hezbollah fires rockets at Israeli-annexed Golan,’ 14 April 2024 or announcements that an Israeli ground offensive in Rafah was imminent.⁷Gaya Gupta, ‘Netanyahu calls Hamas’s demands “ludicrous” and proceeds with plans for a ground invasion in Rafah,’ The New York Times, 15 March 2024 Similarly, the down periods in North Red Sea launches also aligned with broader regional de-escalatory periods, including after the deadly drone strike on an American base in Jordan by Iran-affiliated groups at the end of January, and in mid-April, when efforts were being made to avoid a full-blown war between Israel and Iran.

Expansion and drop-off

Based on the trends of the previous five months, the start of the next phase of Houthi operations could have been expected around March, delineated by a shift to a new location and a new set of targets. But the positions and types of ships attacked remained unchanged through March and most of April, and the tempo of Houthi attacks dropped off during the second half of the fourth phase, with April witnessing the fewest attacks since October. 

The main exception was in mid-March when Houthi attacks briefly intensified, seemingly in relation to Israel Prime Minister Benjamin Netanyahu’s 16 March approval of military plans to enter Rafah.⁸Bassam Masoud, Nidal Al-Mughrabi, and Samia Nakhoul, ‘Israel approves plan to attack Rafah but keeps truce hopes alive,’ Reuters, 16 March 2024 At the same time, Abdulmalik al-Houthi threatened to expand drone and missile launches into the Indian Ocean.⁹Saba Net, ‘The Leader of the Revolution announces the prohibition of ships associated with the Zionist enemy from crossing the Indian Ocean towards South Africa,’ 14 March 2024 However, both military escalations were postponed until the following month when, once again, it appeared that the Rafah operation was imminent, and Iranian-backed groups resumed their attacks on the US and Israel. The Houthis then carried out their first claimed attack deep into the Indian Ocean on 27 April, marking the start of the next phase in the Red Sea crisis.

In the interim between the threatened escalation and the start of the military operations in Rafah and the Indian Ocean, the level of activity decreased, as did the success of the Houthi attacks. The group only struck one vessel in April compared to 13 in January and February — the fewest successful attacks since the first month of hostilities (see graph below), when Houthi operations were focused on the less-achievable target of southern Israel. The group did not conduct a single successful attack on a vessel between 23 March and 26 April.

The drop-off came as tensions in the region were at their highest following the tit-for-tat retaliatory attacks between Israel and Iran from 1 to 19 April that threatened to erupt into a regional war before both sides signaled their readiness to temporarily close the current round of direct conflict.¹⁰Jon Gambrell And Josef Federman, ‘Israel, Iran play down apparent Israeli strike. The muted responses could calm tensions — for now,’ Associated Press, 20 April 2024 Meanwhile, the United States also allegedly made overtures to the Houthis to stop their attacks, including a proposal to lift restrictions on Sanaa Airport and al-Hudayda port and accelerate peace talks.¹¹Mohamad Ali Harisi and Willy Lowry, ‘Yemen Houthis offered US incentives to stop Red Sea attacks,’ The National, 24 April 2024 During the subsequent cooling-off period, there was a lull in Houthi military actions, the longest since the Red Sea hostilities began, as groups in the Iranian-led Axis avoided risking any incidents that could be misconstrued as a re-escalation.

The fluctuating intensity of the maritime attacks throughout the fourth phase has also been closely aligned to broader regional dynamics — in particular, the actions and priorities of Iran in its leading role in the ‘axis of resistance’ against Israel, a trend that looks likely to continue.¹²Sam Dagher and Golnar Motevalli, ‘Iran’s ‘Axis of Resistance’ Watches Israel and Waits for Command,’ Bloomberg, 19 April 2024 Iran’s relationship with the Houthis is a deep-rooted alliance. Tehran has not only supplied weapons, training, and funds but also reportedly shared intelligence and targeting information on the movements of ships in the waters off Yemen.¹³Michael Knights, ‘An Heir and a Spare? How Yemen’s “Southern Hezbollah” Could Change Iran’s Deterrent Calculus,’ The Washington Institute for Near East Policy, December 2023 For their part, the Houthis, while also furthering their own interests,¹⁴Ibrahim Jalal, ‘The Houthis’ Red Sea missile and drone attack: Drivers and implications,’ Middle East Institute, 20 October 2023 have served as a willing partner in the Iran-led attacks on Israel and US regional military assets.¹⁵Samia Nakhoul and Parisa Hafezi, ‘Iranian and Hezbollah commanders help direct Houthi attacks in Yemen,’ Reuters, 21 January 2024

The case of the Behshad

All of these dynamics in both parts of the fourth phase were on display in the role and movements of the alleged Iranian spy ship, the Behshad. The vessel is suspected of being involved in assisting the Houthi maritime attacks, making it a potential target for retaliatory US and Israeli attacks. The positioning of the Behshad has coincided with the locations and tempo of Houthi attacks, as well as the level of regional tensions (see graph below).

The ship had been moored in the Red Sea since 2021 but moved into the Gulf of Aden on 4 January as the third phase drew to a close and the Houthi attacks stretched into the Gulf.¹⁶Financial Times, ‘The mysterious Iranian ship accused of lining up the next Houthi targets,’ 13 March 2024 The Behshad, though, then had to be withdrawn to the relative safety of Djibouti Port, reportedly after being targeted in a US cyberattack as part of a wider retaliation for a drone strike on an American base in Jordan by Iranian-affiliated groups.¹⁷Courtney Kube and Carol E. Lee, ‘U.S. conducted cyberattack on suspected Iranian spy ship,’ NBC News, 15 February 2024 The redeployment of the ship coincided with a reduction in the number and effectiveness of Houthi attacks, as they had less precise targeting information. The group’s operations picked up again with the return of the Behshad in mid-February,¹⁸Dana Polak Kanarik and Boaz Shapira, ‘How Did the Return of the “Behshad” to Iran Influence the Houthi Attacks Against Ships in the Red Sea?,’ Alma Research and Education Center, 24 April 2024 around the same time as Houthi forces struck several commercial vessels.

The Behshad, though, set sail from the Gulf of Aden for Iran on 4 April, a few days after the Israeli bombing of an Iranian consulate in Damascus and a week before the first direct Iranian attacks on Israel, in which the Houthis also participated.¹⁹Patrick Sykes, ‘Iran Ship Linked to Houthi Attacks Goes Home Amid Tensions,’ Bloomberg, 18 April 2024 The removal of the Behshad and de-escalation efforts between Israel and Iran likely contributed to the longest pause in Houthi attacks since the Red Sea crisis began. The group’s maritime activities only restarted in late April once the risk of sparking a regional escalation had subsided, and following back-channel talks between the Houthis and Iranian officials.²⁰Mohamad Ali Harisi and Willy Lowry, ‘Yemen Houthis offered US incentives to stop Red Sea attacks,’ The National, 24 April 2024 It is unclear whether the Behshad’s functions will be served by another ship or by different means.

Looking forward

The Red Sea crisis appears set to move into a fifth phase in the coming month. Based on events during the previous phase, several new trends can be expected:

• The Houthis will likely continue to expand the locations of their attacks, not only targeting commercial ships in the Red Sea and Gulf of Aden, but also stretching into the Indian Ocean. As shipping companies avoid the Houthis’ previous area of operations by sailing further away in the Indian Ocean, drone and missile attacks can be anticipated further afield. 
• Houthi officials have also threatened to target ships in the Mediterranean Sea.²¹Ansarollah, ‘Armed Forces: Ships Arriving At The Ports Of Occupied Palestine Via The Mediterranean Sea Enter The Target Bank,’ 4 May 2024 However, while the group may launch drones and missiles in that direction, their repeated failure to pierce the overlapping network of air defenses between Yemen and Israel over the past six months suggests that a successful attack in the Mediterranean is unlikely to happen in the short term.
• The list of potential targets will also probably be increased again to include ships with an even looser connection to Israel, the US, or the UK. In each phase, the Houthis have enlarged the criteria for targeting merchant ships from those with direct ties to Israel to include any vessel that is sailing to Israeli ports or that is affiliated with the US and the UK. In some instances, ships have been targeted based on incorrect or outdated information.²²Reuters, ‘Houthis mistakenly target tanker carrying Russian oil, security firm says,’ 12 January 2024
• The Houthi maritime attacks seem to have become more linked to regional and international dynamics than domestic concerns — specifically Israel-Iran tensions — and these dynamics will likely be a critical factor going forward. A ground invasion of Rafah, more Iranian-Israeli tit-for-tat attacks, or a ceasefire in Palestine could trigger the next shift in the Houthis’ activities. Over time, the justification for future attacks may grow beyond the Gaza conflict, keeping the threat in the Red Sea as a point of leverage for the group.
• Any re-escalation in the Houthi attacks would prompt reactive US-led strikes on the group’s weapons systems in Yemen, both pre-emptive and planned, resetting the confrontation once again. A re-escalation and expansion in maritime operations and the responsive US-led strikes will heighten the risk of another merchant ship being sunk and civilian casualties, both at sea and on land.

• The expansion of the attacks to the Indian Ocean and the ships being targeted may force commercial shipping to reroute even further away from the Yemeni coast as vessels go to further lengths to avoid the Houthi threat. A successful attack would not only back up the threat, but also possibly extend the high-risk area for commercial shipping, increasing the detours required for safe transits and pushing up costs even higher.