The UAE sent elite commandos to the mountains of Yemen to fight both terror groups, securing critical parts of the country.

The Houthi rebels' actions in the Red Sea off Yemen have had a global impact, cutting transit through one of the world’s most important trade routes by over 50 per cent with attacks on US-led coalition naval ships and civilian vessels – in protest, they claim, at the Israeli war in Gaza.

It’s a crisis that’s barely affected Israel, but elevated food prices in economically struggling countries, disrupting aid to Sudan.

Mr Knights, who recently addressed the UN Security Council on the threat the Houthis pose, has chronicled the UAE’s military campaigns in Yemen amid the 2015 civil war in the country in his excellent 25 Days to Aden. It charts the UAE’s “light footprint“, special forces-led effort to expel the Houthis from the vital port city, spearheaded by local Yemeni allies.

His second book on the conflict, The Race for Mukalla: Arabian Elite Forces and the War Against Al Qaeda, covers the UAE’s 2015-16 struggle, alongside tribal Yemeni fighters and a coalition of other Gulf forces including Saudi Arabia and Bahrain, to defend Marib from the Houthi attack – a vital oil and gas location – and to liberate Mukalla from Al Qaeda.

There, UAE forces excelled in a rugged land that could be described as a graveyard of military intervention, where an Ottoman commander once said armies dissolve like salt in water.

Mukalla, a city of half a million people, had fallen into the grip of Al Qaeda but the militants, who regularly used suicide attacks, were expelled through a combination of smart alliance building, with the coalition engaging with local tribal elites. A similar approach was taken in Aden and Marib.

“What really counted was we sat with them every day and every night, eating, sleeping, talking and training. We knew their families and they knew ours,” a senior Emirati commander told Mr Knights. It was a close bond that propelled the partnership to victory.

A 'masterclass'

What followed was a military assault which quickly wrong-footed the terrorists, sparing Mukalla the destruction often seen in modern urban warfare. The assault is another lesson for the US and Nato allies, after aerial bombardments against ISIS in cities such as Mosul, Ramadi and Kobani.

“A western military would have done a lot more damage going in. One of the reasons there wasn’t so much damage, and why the adversary wasn't so formidable, is because of the speed with which the operation was planned, launched and executed,” Mr Knights says, calling the effort a “masterclass” in counterterrorism.

While global attention focused on the fight against ISIS in Iraq and Syria in 2016, local Al Qaeda forces, taken on by the UAE, were the same militants who bombed the USS Cole in 2000, killing 17 sailors. They also plotted bombings on commercial flights and cargo planes.

On the flank of Mukalla, vital infrastructure around Marib was defended from the Houthi rebel offensive and vast quantities of their military equipment were destroyed, leaving the group weaker today.

Mr Knights describes the group as a fanatical enemy ready to fight to the death for their supremacist cause.

Covering recent events, the books offer profound lessons for the current crisis, where the Houthis are proving resilient to US and British air bombardment and, increasingly, Israeli strikes as they seek to widen the regional crisis. Without more focused action with local allies, aid efforts and a long-term military strategy, Mr Knights warns, the rebels will endure.

None of this means the situation is doomed, he says. The UAE has shown how to execute such a campaign successfully in a way that might ease the minds of those fearful of another Afghanistan or Iraq, where years-long counterinsurgency campaigns ended in calamity.

“Counterinsurgency has become synonymous with quagmire,” Mr Knights says, but the UAE showed what can be achieved with a blend of local engagement and small teams of advisers.

“In the West, we're very suspicious of the idea that we can build local forces. The Emiratis are excellent at building local forces. And what is the trick to that? The magic is that they build forces that are good enough. They're not clones of western forces. They're intended to be substantially better than the force that they're attacking. And they support them, over the shoulder with ‘accompany, advise, assist, enable‘, and they stay with them for a long time.”

The Emiratis avoided the trap the Egyptians had fallen into in the 1960s, when former president Gamal Abdel Nasser referred to his war in Yemen as “my Vietnam“, due to the heavy losses incurred securing the country’s rugged terrain.

Historians of Yemen often point out it may be one of the hardest places to fight. Amid long-dormant volcanoes and mountains with few reliable roads, Emirati commandos manoeuvred into battle, often at night, carefully driving near cliff edges with headlights off, wearing night-vision goggles.

Towering high ground provided hardy caves and dugouts for cover, as well as vantage points for an ambush – battles recounted in gripping parts of the book were based on many witness interviews.

In remote villages and towns, tribes rapidly shift allegiances, communities that suffered decades of conflict have become experts at self-preservation. The UAE managed this complex struggle with small units of elite fighters, what Mr Knights describes as “an extraordinarily light footprint“, but where necessary, heavy air power and tanks.

This complexity is brilliantly described, from tribal intrigue in a land where few Yemenis knew who to trust, to the nightmare of modern conflict where night vision and drones provide nowhere to hide.

“The UAE showed it could “prosecute the main war against the Houthis in parallel to the counterterrorism struggle against Al Qaeda”, Mr Knights says. Much of the country appeared lost in the chaos of state collapse.

“The UAE doubled down when things looked as if they were impossible. This was the choice they faced: ‘Do we accept that and back off and let the Yemenis defend themselves in Aden? Or do we double down and continue with the effort to remove the Houthis from Aden and race them to Mukalla?’ The choice is fundamentally, do we just fight the main enemy, the Houthis, and do we turn a blind eye to what Al Qaeda is doing? Or do we fight and defeat both? And they chose to defeat them both.”

“This concept of having to fight a war within a war is increasingly relevant. Wherever we're fighting, we might have a main enemy, like the Iran Threat Network, but at the same time, we have other forces trying to gain an advantage within a war-torn environment, like Al Qaeda. We see that in the Horn of Africa. We see it in Syria, we see it in lots of different places. We do the counter-ISIS fight in Iraq and Syria at the same time as we're fighting Iran-backed militias who are attacking us.”

“So fighting these wars within wars, it's very interesting, and it's very timely. The Houthis, as the UN panel of experts has certified, are working increasingly closely with Al Shabab, with Al Qaeda.”

Mr Knights is working on a third book, on the 2017-18 battle for Hodeidah, to be released later this year, completing a trilogy covering much of the anti-Houthi intervention in support of Yemen’s internationally recognised government.