Yemen’s Houthis are going underground
Analysis by the IISS of satellite images shows that the Houthis are digging in, creating new and much larger underground military facilities that could bolster their protection in case of future conflict.
The (Houthi) movement in Yemen is digging in for the long term, literally.
The armed group, which controls much of the country and has been harassing shipping in the Red Sea, has undertaken a major expansion of underground military facilities, satellite images reviewed by the International Institute for Strategic Studies reveal. The building boom predates the ongoing United States-led Poseidon Archer military operation that has targeted the Houthis to counter their attacks on cargo and military vessels.
While the Houthis used caves and simple tunnels in their earliest days as an armed group, more recently, they have pursued much larger installations, refurbishing both pre-war Yemeni Army tunnel systems and building entirely new underground facilities.
The construction efforts illustrate that even before the military confrontation with the US and allied forces, the Houthis were preparing for, and hardening themselves in case of, future conflict.
Building blocks
Some of the first evidence that the Houthis were using underground facilities emerged in 2004, during the first of the so-called Saada Wars between the Yemeni government and what was, at the time, a peripheral northern Yemeni rebel group. In September of that year, the Yemeni army killed the group’s first leader, Hussein Badreddin al-Houthi.
According to Houthi sources, Yemeni army forces discovered the cave in which he was hiding and poured gasoline into it before setting it ablaze. Leadership passed to Hussein’s brother, Abdul Malik al-Houthi, who continues to rule the group. It also set the stage for more than six years of insurgency against the government of then-president Ali Abdallah al-Saleh and seven subsequent years of war against the Saudi Arabia-led coalition, which intervened in Yemen in 2015 to stop and reverse Houthi advances, during which the Houthis reportedly made extensive use of natural caves and smaller tunnels across Yemen’s rugged, mountainous landscapes.
The Houthis, however, were not the first to introduce underground facilities to Yemen. The Saleh government (1978–2012) constructed large underground facilities, some of them associated with military installations and others reportedly intended for the personal safety of high-ranking government members and assets. Several such sites were discovered following the fall of the Saleh regime. After the Houthis took over the capital, Sana’a, and large parts of northern Yemen in 2014 and 2015, a Saudi-led coalition began an aerial campaign against the Houthis and allied factions in March 2015. Early in that campaign, former Yemeni military facilities now under Houthi control became prime targets for the adversary coalition forces, which struck entrances to many Saleh-era underground facilities relatively precisely.
The first major Houthi building period began in the late 2010s, as the pace of coalition airstrikes markedly decreased. Houthi forces moved beyond smaller tunnel designs and began refurbishing Saleh-era underground facilities. Satellite imagery shows debris being cleared from tunnel entrances, new vehicle tracks leading into the tunnels as well as the presence of construction vehicles at the al-Hafa military base, the former Presidential House and the Yemen television compound in Sana’a, and the military storage facility near ad-Dabr. The appearance of large piles of excavation waste, also known as spoils, indicates that the work at al-Hafa might have included a significant expansion of the original facility. In at least two cases, the renewed work on these sites led to another round of strikes on al-Hafa and the Yemen television compound by the Saudi-led coalition in 2020 and 2021.
Building boom
After the Houthis agreed to a truce with the Saudi-led coalition in April 2022, which has largely held, they embarked on a more expansive construction effort that went beyond refurbishing and expanding existing Saleh-era underground facilities. Satellite imagery shows at least two new underground facilities built by the group.
In late 2022, the Houthis began work on a new facility in a valley near their local stronghold of Saada. As of February 2024, satellite images show three tunnel entrances wide enough to accommodate heavy vehicles and large piles of excavation waste at the site. Two more sites near Saada showed features consistent with military-underground-facility construction but cannot be conclusively identified as such.
Work also took place at a former Yemeni Army Scud missile base at Jabal Attan in Sana’a. The Houthis, in the first half of 2023, began constructing a large tunnel, suggesting that work on a large underground facility was under way.
Foundation for fighting
The fact that the Houthis began constructing major new installations after the agreement of the ceasefire with the Saudi-led coalition suggests that the group is focused on entrenching themselves and bolstering their military capabilities. The resilience of the sites in the face of Saudi and coalition-partner air strikes may have even enhanced the Houthis’ interest in them.
The group opted to construct large installations visible on satellite imagery rather than exclusively adhering to the clandestine mode of tunnel construction favoured by groups like Hamas and Hizbullah. The size of the entrances, which are large enough to accommodate heavy vehicles, raises questions about whether these refurbished and newly constructed underground facilities could eventually be used to conceal parts of the Houthis' strategic-missile and UAV arsenal.
The resilience of the underground facilities is now being tested. The US Department of Defense has said that it has struck underground targets as part of operation Poseidon Archer.
