LONDON, Sept 17 (Reuters) - A lightning advance by Yemen's Houthi group has brought the vital Bab el-Mandeb Strait under its control, making the once ragged highland militia a regional player with global clout.

This is how the group evolved into a formidable fighting force with Iranian support that can disrupt vital shipping and strike critical oil and gas facilities in neighbouring Saudi Arabia.

WHO ARE THE HOUTHIS?

Starting out in the late 1990s as a Zaydi Shi'ite Muslim revival movement in north Yemen under theHouthi family, the group waged six wars against the government, building a strong local militia.

When Yemen's central state disintegrated during the 2011 Arab Spring, the Houthis took advantage, gaining more ground and developing a relationship with Iran and its Lebanese ally Hezbollah.

In 2014 they seized the capital Sanaa, ousting the government, and halting a Gulf-backed political transition.

That prompted a Saudi-led military intervention to support the government, leading to years of civil war that ground to a stalemate and a 2022 ceasefire.

The Houthis fired missiles and drones at Israel and international shipping in the Red Sea during Israel's war in Gaza from 2023-25 in what they said was solidarity with Palestinians.

With their closest ally Iran under attack by the United States since February 28, the Houthis have again been firing on Red Sea shipping as well as energy facilities inside Saudi Arabia.

WHAT IS THE MILITARY SITUATION INSIDE YEMEN?

The ceasefire collapsed over recent weeks and fighting resumed along the old front lines: Marib and Jawf governorates in the north, the city of Taiz in the southern highlands, Dhale in central Yemen and the Red Sea coastal strip known as the Tihama.

Last week the Houthis rapidly advanced into the southern Tihama, seizing first the port city of Mocha and then the rest of the Red Sea coastline and islands, putting their guns along the whole shore of the 12-mile-wide (19-km-wide) Bab el-Mandeb Strait.

Those territorial gains make it easier to block shipping on the Red Sea, a key route for Saudi oil exports to Asia, and set up a potential launchpad for a new ground thrust towards Aden.

Saudi Arabia has conducted airstrikes in support of government-aligned forces.

WHAT DO WE KNOW ABOUT HOUTHI MISSILES AND DRONES?

The group's ability to strike at distance with growing accuracy is why it now matters far beyond Yemen.

Houthi ballistic missiles have reached as far as Israel, more than 1,000 miles (1,800 km) away, and one struck the perimeter of Israel's main airport in 2025. They have struck more frequently in Saudi Arabia, targeting cities and infrastructure. And Houthi missiles have been fired at ships in the Red Sea, halting traffic in the waterway.

Houthi drones have also struck repeatedly at Saudi targets and are now increasingly deployed on the battlefield — a big change from the last bout of civil-war fighting before the 2022 ceasefire.

WHAT EQUIPMENT HAVE THE HOUTHIS BEEN SEEN USING?

The Houthis have posted videos online since the start of September that show some of the military equipment they are using.

Videos show drones dropping different types of mortar and other bombs onto vehicles and opposition fighters, a rocket or missile launching, and precise munition hits on buildings and trucks at a camp, filmed by a high-resolution drone.

Other videos show Houthi forces on the ground including in pick-up trucks, some mounted with weapons, and on foot. Many fighters are shown in Arab robes rather than uniforms and carrying assault rifles. One video also showed a small group of fighters in camouflage uniforms. In some videos, fighters are shown with light and heavy machine guns and scoped rifles.

Videos showed them parading equipment captured from the Saudi-backed forces in the Tihama including armoured and combat vehicles, a tank, an artillery gun, satellite dish, small arms and a drone jamming device. But the videos do not generally show the captured hardware in action.

HOW DO THE HOUTHIS GET THEIR WEAPONS?

A United Nations panel of experts' report in 2025 said the Houthis had developed missile and drone technologies through both technical assistance and domestic manufacturing.

It found there had been widespread arms smuggling despite a U.N. arms embargo, including overland shipments across the Omani border as well as seaborne smuggling.

Items seized included drone control devices, equipment to receive ships' navigational data, drone engines and missile components. A 2023 U.N. report noted seizures of entire drones, ballistic missile components such as chemical precursors and Iranian-made anti-tank missiles.

Iranian sources have said Tehran has supplied its Houthi allies with both weapons and experts. However, Iran has officially denied arming the Houthis in violation of the U.N. arms embargo.

A 2025 assessment by the International Institute for Strategic Studies think tank found that while the Houthis had made advances in domestic arms production, they remained dependent on Iran for key technologies and advanced capabilities.

IN WHAT OTHER WAYS HAVE THE HOUTHIS DEVELOPED MILITARILY?

The U.N. panel of experts' report described Houthi military tactics as being focused on infiltration, drone attacks and shelling along front lines, and the laying of mines and other explosive devices.

They assessed that the Houthis had 350,000 fighters, partly through the recruitment of fighters under 18.

Training by Iran and Hezbollah has been critical for the Houthis, according to Yemen analysts. Baraa Shiban, an associate fellow at the Royal United Services Institute in London, said such training had begun soon after the Arab Spring and had helped the Houthis transform from a militia to a more organised military force with changes to their structure and movements.

Hezbollah missile and drone operatives were present with the Houthis in 2025, the U.N. experts said. Iranian Qods Force general Abdolreza Shahlaei was also present in Yemen for some time working with the Houthis, the experts said.

(Compiled by Angus McDowall and Edward Carron, Editing by Timothy Heritage)