The United States should not interfere in the campaign, which has begun and stands a good chance of succeeding, except through steps to make the operation quicker and less destructive.

This PolicyWatch is the second in a three-part series on the Red Sea campaign in Yemen. Part 1 covered the strategic risks and opportunities inherent in cutting off Houthi access to the sea. Part 3 discusses the Houthis' options for broadening the war if their access is threatened.

Yemeni forces backed by the United Arab Emirates are now beginning a 100 km advance on the last Houthi-held ports on the Red Sea—Hodeida and al-Salif—and Saudi-backed Yemeni forces are positioned to pressure those areas from 140 km to the north. A key uncertainty for U.S. policymakers and humanitarian agencies involves the feasibility of a new Yemeni offensive to reach Hodeida and al-Salif, and then capture intact these vital food-importing ports.

MILITARY GEOGRAPHY OF THE RED SEA COAST

The Tihama region of Yemen comprises a strip 50 to 70 km wide running along the Red Sea coast from the Bab al-Mandab Strait to the Saudi border. Hodeida, Yemen's principal Red Sea port, is located about halfway up the coast. Al-Salif, the other key Red Sea port, and the nearby Ras Isa oil-export terminal are both located on the peninsula 60 km north of Hodeida.

In contrast to the rugged highlands of central Yemen, the terrain of the Tihama is overwhelmingly flat, covered by sandy desert cut by west-east "greenbelts," strips of dense low-lying scrub, palm groves, and farms situated along the wadis running down from the central highlands. Many small towns and farms dot the landscape. Two main north-south highways run the length of the Tihama plain—one on the coast and one paralleling the coast 50 km inland. The two key ports now held by the Houthis present very different operational challenges to a liberating force:

Hodeida is a midsize, 5-by-6-km city with a population of likely more than 700,000. The Hodeida port is located on the northern edge, just outside the main urban area. A densely populated old city measures about 1.5 by 1.5 km. To the immediate southeast of the city is a 50-square-km heavily vegetated "green zone"—in Yemeni military parlance—but this area can be bypassed to the west and east along highways and through open desert. No high ground exists immediately east of the city, into which the Houthis could potentially fall back: in fact, the nearest mountains are 110 km to the east. In terms of human terrain, Hodeida is primarily populated with urban and coastal people of the Shafi'i sect, not the mountain Zaidi sect clans that make up the Houthis' reliable fighting cadres. The Houthis are foreign occupiers and likely to number fewer than 5,000, while the 22,000-strong Yemeni resistance forces marching on Hodeida have strong connections to the area, including large numbers of Tihama coastal fighters with family ties to the city.

Al-Salif port is located on a lightly populated, sandy peninsula jutting out into the Red Sea 60 km north of Hodeida. The port features two deepwater berths and a large grain-loading terminal. The Ras Isa oil-loading terminal, the coastal terminus of the Marib oil pipeline, is located at the southern tip of the peninsula. The Houthis have laid extensive minefields and trench networks on the peninsula, but the area is open, providing no cover from aerial attack, and the Houthis would likely abandon it if faced by advancing forces that threatened to cut off the peninsula.

HOUTHI DEFENSIVE CAPABILITIES

The Houthis rely on a small cadre of hardened fighters from their core governorates of Saada and Amran, in northern Yemen. These troops are highly dedicated, and their near-fanatical bravery is bolstered by religious belief, clan loyalty, and the use of amphetamine stimulants such as Captagon (fenethylline). On the Red Sea front, these cadres are assessed by Yemeni intelligence to number fewer than one thousand. To fill out the Tihama frontline, the Houthis have impressed into service up to four thousand tribal levies and child soldiers from the Tihama and the highland governorates of central Yemen, often by compelling tribal leaders with threats of violence. The morale of this impressed manpower is low, and such fighters frequently abandon the Houthis when not under direct supervision.

The Houthis had adapted to the persistent presence of loitering Gulf coalition aircraft and drones by fighting in a highly dispersed, low-density style: cells of ten to twelve fighters frequently occupy frontage of a dozen kilometers, and teams of two to three fighters are responsible for holding a hill or farm and its surrounding area. A small number of Houthi fighters can cover a large frontage by filtering up to the frontline without carrying weapons, fighting from prepositioned caches, and periodically occupying and then abandoning parts of the previously prepared system of defensive fortifications.

Houthi defensive resilience is closely linked to terrain, with Houthi troops defending much more successfully in mountain areas, where they feel confident and secure. On the flat Tihama plain, the Houthis have utilized the dense bush cover of the greenbelts to build an extensive system of defensive fighting positions, including trench networks, small underground bunkers, and prepositioned weapons and ammunition caches. They frequently use areas of dense vegetation to conceal mortar positions or howitzers and even the occasional T-55 tank. As on other frontlines, the Houthis have covered off-road approach corridors along wadis and dirt tracks with unmarked harassment minefields, and seeded the shoulders of paved roads with IEDs, including explosively formed penetrators and claymore-type devices camouflaged with painted foam to resemble rocks.

The Houthi record in defending large urban areas has been mixed, and such defenses have generally faltered—although admittedly they may try harder to defend their "cash cow," Hodeida. In 2015, the Houthis fought a protracted four-month urban battle in Aden (population 1.7 million) against the newly formed Yemeni resistance, which was supported by very small numbers of UAE special forces. Yet the Houthis crumbled in less than a week when the UAE provided mine-resistance ambush-protected (MRAP) vehicles to trained Yemeni units and mounted a well-planned scheme of maneuver. In Taizz (population 900,000), the Houthis have not defended the city per se but rather the mountains that closely tower over it. In fights for smaller towns on the Tihama front such as Mokha, al-Khokha, and al-Hays, the Houthis have performed similarly, fighting hard for several weeks in layered defensive positions outside the urban areas, and then collapsing and falling back several kilometers, returning only to harass the newly recaptured towns with rocketfire. Indeed, when faced with rapid attacks from multiple directions threatening their rear logistics routes, Houthi forces frequently abandon their positions and melt away to regroup in areas of rugged terrain.

PROSPECTS FOR A BREAKTHROUGH OFFENSIVE

An operation to retake Hodeida would entail a 100 km advance by UAE-backed Yemeni forces up from their current positions at al-Hays and al-Khokha. The offensive would need to push through a number of "green zones" from which small cells of Houthis would mount persistent harassment attacks on Yemeni lines of communication. This would not present insurmountable obstacles to the UAE-backed Yemeni forces, which include powerful UAE armored units mounted in up-armored Leclerc main battle tanks, supported by extensive air, drone, and artillery systems. Indeed, the UAE has supported other long-range Yemeni advances:

In the breakout from Aden in July and August 2015, a UAE-led battle group punched up from Aden through Lahij city to al-Anad Air Base in less than ten days, a rate of advance of around 4 km per day in terrain similar to the Tihama.

In 2017, Tihama resistance forces supported by a UAE battle group achieved a similar rate of advance during its thrust up the Red Sea coast, advancing the 58 km to Mokha and al-Khokha in about a week.

An operation involving an amphibious component, as in Aden in 2015, would likely substantially reduce the timeframe required to retake the port and other key locations.

Similarly, the Houthis might offer less resistance if Saudi-backed Yemeni forces also advanced southward from Midi, 170 km north of Hodeida.

Getting to Hodeida is, thus, not the major obstacle. Seizing the port may also not be as difficult as many observers expect, considering its slight remove from the city and its fairly open layout. The UAE has quickly fortified and provided missile defense for all the locations it has helped liberate so far. The UAE has also used state-owned shipping and military engineering capabilities to immediately get ports operating in Aden, al-Mukalla, Bab al-Mandab, and Mokha. In Aden in 2015, for example, the UAE drew on its extensive port management and logistics expertise to reopen the port in less than a week.

Nevertheless, it will be difficult to convince commercial shippers to stop at a port that is receiving sporadic retaliatory harassment from rockets and mortars. Encouraging such traffic would necessitate clearing a broader perimeter around the port, including the urban area. Yet clearance of Hodeida's urban area might result in a protracted fight lasting up to four weeks if the Houthis defend strongly. Just as likely, though—taking Aden as an example—the Houthis may evacuate owing to their small numbers vis-à-vis an unfriendly local population. An urban clearance is likely to be conducted primarily by the 22,000-strong local Tihama resistance plus Adenese Salafi forces trained and equipped by the UAE, with Emirati forces providing logistics, intelligence, and selective artillery and air support.

IMPLICATIONS FOR U.S. POLICY

Strong evidence suggests that the UAE-backed Yemeni forces can successfully advance on Hodeida and al-Salif, and, based on prior cases, they have a good chance of capturing their ports intact and getting them operating immediately after a battle. Houthi resistance in the Tihama plain is weakening by the day, and the Houthi fighters are alien to the area and its people. When liberated, the ports will be able to receive more food relative to the present, and international agencies should attribute full blame to the Iran-backed Houthis if they tax or obstruct food and fuel delivery into northern Yemen. Humanitarian agencies would be able to work in Hodeida without fear of either Houthi intimidation or collateral damage related to the coalition air campaign. The Red Sea coast and the Bab al-Mandab Strait would also be free of the threat of Houthi sea mines, antishipping missiles, explosive drone boats, and other attacks. These are all outcomes the United States should support.

The key guiding principle for the U.S. government should be to "do no harm"—in other words, to stay out of the way of the UAE-backed Yemeni liberation of Hodeida, al-Salif, and the entire Red Sea coast. Washington should work with other capitals and international organizations to publicly warn the Houthis against any scorched-earth tactics in the ports that could slow their development as food-import locations. If possible, the United States should transmit useful intelligence to the Yemeni government and Gulf coalition that might reduce the destructiveness and duration of the Tihama campaign, which could—in a worst-case scenario—render Hodeida and al-Salif inactive for months and tip northern Yemen into famine. The United States is already conducting such surveillance for its own situational awareness, and the moment may be right to operate a fusion cell specifically to ensure that timely warnings of scorched-earth tactics or other threats can be communicated to the Yemeni forces moving to liberate the Red Sea ports.

Alexandre Mello is the lead security analyst at the risk advisory firm Horizon Client Access and recently spent two weeks in Yemen on the Tihama front. Michael Knights, a senior fellow at The Washington Institute, just returned from a visit to Yemen's battle fronts, where he received detailed briefings from Yemeni and Gulf coalition officers.