Introduction

On 23 August, the Houthis, a Yemen-based rebel group, attacked a Greek-flagged vessel in the Red Sea, causing an oil leak and threatening an environmental catastrophe in one of the world's most frequently used waterways. On 2 September, the group attacked a Saudi and a Panama-flagged oil tanker in the same sea area- using a combination of missiles and one-way attack drones.

These attacks are part of a broader campaign carried out by the Houthi rebels since Israel's war on Gaza that involve hybrid maritime warfare.

Since October 2023, the Yemen-based group has attacked more than 100 commercial and military ships in the Red Sea. The Houthi movement claimed that they viewed any vessel connected to Israel or heading to or from there as legitimate targets. However, in practice, they have conducted indiscriminate attacks on ships from various nations.

Hybrid Maritime Warfare

The Houthis' actions perfectly align with what leading US defence intellectual Frank G. Hoffman once called hybrid maritime warfare. Hoffman has defined hybrid maritime warfare as 'a form of warfare combining asymmetric naval tactics, sophisticated weapons, and terrorist activity'. He argued that Iran and Iraq's systematic attacks against merchant vessels in the late 1980s, which became known as the Tanker War, exemplified maritime hybrid warfare.

A non-state armed group, the Houthis, has now adopted this method of warfare. The Houthis possess advanced military capabilities, including anti-ship cruise missiles, ballistic missiles, aerial drones, and uncrewed naval drones. The group has primarily targeted commercial vessels in their attacks, with these actions against Red Sea shipping clearly constituting maritime terrorism. They have also attacked military ships.

In early March, the rebels used naval missiles and drones against several American and allied warships in the Red Sea. Such attacks can be classified as guerrilla warfare at sea.

The group's combination of advanced conventional capabilities with asymmetric naval warfare tactics - characterised by surprise attacks on enemy ships and efforts to avoid military response - represents a hybrid maritime threat. But who are the Houthis, and what drives them to pursue such a campaign?

Who are the Houthis?

The Houthi movement, also referred to as Ansar Allah (supporters of God), is a Yemen-based armed political and religious organisation associated with and acts on behalf of the country's Shia Muslim minority, the Zaidis. The Houthi rebels captured Yemen's largest and capital city, Sana'a, in 2014 and have since waged a fierce and protracted civil conflict against the Yemeni government, which is itself supported by the Saudi-Arabia-led Sunni alliance.

The Houthis currently wield substantial political power in Zaidi-majority areas of Yemen.

Why are the Houthis attacking ships at the Red Sea?

The Houthis, alongside various non-state actors, including Hezbollah, Hamas, and Kata'ib Hezbollah, identify themselves as part of the Iranian-led 'axis of resistance' against Israel and the United States. Since Israel's war on Gaza, the rebel group has fired more than 200 drones and cruise missiles at Israeli territory to show its solidarity with Hamas.

Houthi leaders have repeatedly warned of escalating and more sophisticated military assaults against Israel, calling for an end to Israel's brutal war on Gaza. As previously noted, the Houthi rebels have also carried out attacks against dozens of merchant and naval vessels in the Red Sea, regardless of their connection to Israel or its allies.

These actions aim to disrupt international shipping and create anxiety among countries that support or at least do not contradict Israel's actions in the Gaza Strip.

The Houthis and Iran

The main factor giving the Houthis access to advanced weapons is their close ties with Iran. The Houthi movement engages in sectarian geopolitical projects in alignment with Tehran's pursuit of regional hegemony. In return, Iran has large...