The armed men drove right into the nighttime ambush. The militants, led by a veteran jihadist blamed for a bloody attack on Westerners just 10 days earlier, were winding their way along a narrow desert road in central Tunisia.

When the elite Tunisian forces hidden in the surrounding hills opened fire, their tracers lit up the night sky, and some of the militants tried to flee. All nine suspects, including the senior militant, Khaled Chaib, were killed. An informant in the truck at the time of the ambush was wounded in the shoulder.

The March 2015 operation was a badly needed victory for Tunisia’s fragile democracy, whose leaders were struggling to deliver on the promise of the 2011 revolution. Prime Minister Habib Essid called the ambush by Tunisian National Guard forces the crowning success of a growing counterterrorism capability. One newspaper headline proclaimed: “The country has been saved from catastrophe.”

But what Tunisian leaders did not reveal was the pivotal role that U.S. Special Operations forces had taken in helping to design and stage the operation.

According to Tunisian and U.S. officials, American communications intercepts tracked down Chaib, an Algerian also known as Loqman Abu Sakhr, allowing the local troops to position themselves in the desert. An American team, made up of Special Operations commandos assisted by CIA personnel, helped the Tunisian forces craft and rehearse the ambush. And while the raid unfolded, an American surveillance aircraft circled overhead and a small team of U.S. advisers stood watch from a forward location.

Speaking by telephone, Gen. David M. Rodriguez, the head of U.S. Africa Command, praised the counterterrorism efforts of Tunisian forces but declined to comment on the operation in Tunisia’s Gafsa region. The CIA also declined to comment.

The operation illustrates the central but little-known role that U.S. Special Operations troops can play in helping foreign forces plan and execute deadly missions against militant targets.

In recent years, U.S. forces have provided this kind of close operational support – a range of activities including what’s known in military parlance as “combat advising” or “accompany” and “enabling” assistance – in a growing list of countries beyond the active battlefields of Iraq and Afghanistan, including Uganda, Mauritania, Kenya, Colombia, the Philippines and Tunisia.

Those activities have taken on greater importance as the Obama administration has scaled back the direct combat role of U.S. troops overseas and instead sought to empower local forces to manage extremist threats.

At the same time, the strategy, while low-risk to Americans, has done little to change the overall security picture in countries with deep political and economic problems. It is an approach that some analysts say may provide the partner forces – and the United States – with a false sense of security while having little lasting effect.

Much of this hands-on support has taken place in Africa, where the growth of militant groups, often allied with al-Qaeda or the Islamic State, has outpaced under-equipped and under-trained local militaries.

“There is still this misunderstanding that we have one mode which is combat, and another mode which is [training],” said Linda Robinson, a scholar at the Rand Corp. who tracks U.S. Special Operations activities. “There’s this whole spectrum in between, which is operational advise and assist.”

In that role, American forces help partner forces plot out risky operations, which are often enabled by U.S. hardware and intelligence, including spy planes and other advanced intelligence systems. U.S. aircraft have flown foreign forces to the site of an operation or stood by to evacuate casualties. In certain cases, U.S. troops are authorized to act as combat advisers, accompanying foreign forces into battle and stopping just short of the front lines.

The operations differ from the U.S. “direct action” missions such as the 2011 assault on Osama bin Laden’s Pakistan hideout or the 2014 raid to rescue American hostages in Syria.

In those operations, President Obama has proved willing to risk American lives to capture or kill a high-value militant or rescue hostages. But he has also instructed his military leaders to look for opportunities for indirect U.S. action, which puts both the risk and the glory on partners’ shoulders.

“This enables them to take those responsibilities themselves and reduces what are often very politically sensitive issues,” said a senior U.S. defense official who, like others, spoke on the condition of anonymity to discuss delicate operations. “It reduces our footprint, our presence, and it gives credit to the [partner] country.”

William F. Wechsler, who was a senior Pentagon official overseeing Special Operations activities until last year, said that preparing foreign forces to carry out assaults, rather than a direct U.S. strike, involved a balance between long- and short-term objectives.

“It’s almost always easier for U.S. forces to do it directly,” Wechsler said. “But if your wider mission is to build up the capabilities of our partner, you accept some risk to mission and support local forces doing it.

“Done right, this becomes a virtuous cycle.”

The partnerships, which typically involve small Special Operations teams, are seen as a lower-risk, lower-cost approach than the massive programs that former president George W. Bush launched to rebuild the militaries of Iraq and Afghanistan. Those experiences created lasting doubts at the Pentagon about the United States’ ability to transform foreign forces.

In Afghanistan, the shortcomings of local troops may prompt the White House to once again delay Obama’s troop withdrawal. In Iraq, the army that American troops trained at a cost of more than $20 billion collapsed to advancing Islamic State fighters in 2014.

“This is one of the big debates right now: Does this work?” Robinson said. “A lot of people have been pessimistic about the U.S. ability to build partner capacity and whether it has been able to take care of the security threat.”

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Military officials said the growth in programs providing hands-on support to foreign operations grew out of earlier experiences in places such as Mali, where U.S. Special Operations troops trained and did exercises alongside local forces between 2005 and 2009. After conducting training exercises, U.S. officials were disappointed to watch Malian troops stumble in battle.

“That was one of the lessons learned, that . . . we probably would be more effective if we stayed with them,” the defense official said. “You’re trying to bring guys from a pretty basic place in terms of their knowledge set and give them some advance skills, and then you’re tossing them into the deep end of the pool.

“So it sort of evolved, and we began to ask for the authorities to stay with them,” the official said.

Pentagon officials describe the ongoing U.S. mission in Somalia, where Special Operations forces are advising troops from the African Union Mission in Somalia (AMISOM), as a successful illustration of this kind of operational support.

Although the United States had trained AMISOM troops in their home countries in the past, officials realized those forces needed extra help when they faced the militant group al-Shabab. U.S. troops now help allied forces in Somalia plan and execute missions. They provide aerial surveillance and, under authorities that allow them to protect partner forces, conduct airstrikes against militants.

The African troops “do the bulk of the work, but we’ve been able to help them through particularly tricky problems they may have,” the official said.

While U.S. officials say the strikes reflect the increasing scope of AMISOM activities, the attacks also point to the continuing strength of al-Shabab fighters even after they were dislodged from major Somali cities.

Mark Mitchell, a former White House official and Green Beret who worked closely with local forces in Iraq, said that sending U.S. troops on missions with local forces allowed opportunities for training and mentoring, including on human rights. It also ensures efficient exploitation of evidence obtained during operations, he said, and increases the confidence of local forces.

“They know Americans are not going to be left out to dry,” he said. “So if things go badly, we’re a security blanket for them.”

But even missions that are not supposed to expose U.S. troops to combat can bring deadly risks.

The renewed U.S. mission in Iraq suffered its first combat casualty last year when a Delta Force soldier was killed during a mission accompanying Kurdish peshmerga troops. Although American forces were supposed to remain in a supporting role, Master Sgt. Joshua Wheeler became engaged in a firefight when he came to the defense of the Kurds.

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The broader effect of U.S. support, even if it can hone the skills of foreign counterterrorism forces, has at times amounted to little when assistance is too narrowly focused on small, elite units.

In Yemen, a long-running combat advisory mission was halted after the disintegration of the government at the end of 2014. After U.S. Special Operations troops departed abruptly several months later, the United States’ ability to counter al-Qaida in the Arabian Peninsula was severely curtailed. U.S. officials were unable to account for hundreds of millions of dollars in fighting gear provided to local forces.

The experience with combat advising in Yemen highlights the risk that U.S. training may succeed in building up the tactical ability of those forces for a period of time but fail to shape the larger security organizations or political environments in which they operate. Without broader changes to military leadership, systems to equip and pay troops, or efforts to tackle corruption, the impact of U.S. help can quickly vanish.

“Here’s where the downfall or flaw is,” Mitchell said. “The minute we leave the organizations that we create . . . they have a half-life. After about a year, that capability we built is squandered, and it’s back to square one.”

Robinson said a long-running American advisory mission in the Philippines, where U.S. troops helped local forces plan missions against Abu Sayyaf and other militant groups, had managed to avoid that transition problem by spreading training across a wide array of Philippine units. That mission concluded in 2014.

“It was also pretty carefully done so U.S. forces wouldn’t end up inadvertently in the front line fighting the fight,” meaning local units were forced to gain their own skills, she said.

In Tunisia, officials were forced to grapple with intensifying security threats after the 2011 revolution. The security services that former dictator Zine el-Abidine Ben Ali had employed to keep tabs on Tunisians struggled to contain growing radicalization, which spread in the country’s newly permissive environment. Chaos in neighboring Libya allowed jihadist groups to gain strength.

“You have so many different types of threats that intersect in Tunisia, with limited resources to address it,” said Haim Malka, a senior fellow at the Center for Strategic and International Studies in Washington. “It’s overwhelming.”

On March 18 last year, the costs of insecurity came into stark relief when a small cell of attackers stormed the Bardo, the famed national museum in Tunis. At the end of the siege, at least 20 people, mostly Western tourists, were dead.

The bloodshed at a beloved national monument was a stunning blow to the country’s tourism industry and, since at least one of the gunmen was known to local authorities, an indictment of the government’s ability to keep people safe.

Although the Islamic State claimed responsibility for the attack, the government pointed the finger at Chaib’s group, al-Qaida-linked Okba Ibn Nafaa, which had also launched repeated attacks on Tunisian forces.

After 2011, Tunisia’s new democratic leaders knew they needed help. Officials asked allies, including the United States and Germany, to help tighten the border with Libya. U.S. military personnel, who number up to about 100 in the country at a time, are also training national guard and army special forces soldiers.

The United States arranged to provide ScanEagle surveillance planes to Tunisia; the Tunisian government is also waiting for Black Hawk helicopters that it purchased. In a recent interview in Tunis, President Beji Caid Essebsi said that U.S. support is valuable but that more is needed.

“If our friends are keen to help us, we will be happy,” he said.

But officials there, mindful of Tunisians’ feelings about foreign involvement, want to play down any perception of overt U.S. military involvement. “The Tunisian government has to be careful about being seen as working too closely with the United States,” Malka said.

According to a Tunisian security official, the low-profile U.S. assistance was critical in staging the Gafsa mission. The Americans “provided the training and supported the operation” with intelligence and other means, the official said. U.S. forces also helped rig the vehicle that militants drove into the ambush.

The day after the raid, Tunisia’s Interior Ministry hailed the operation, showcasing photos of the dead men, splayed in the truck or lying on the rocky ground.

“The operation was intended to kill them,” the official said. “We did not intend to arrest them.”

(c) 2016, The Washington Post · Souad Mekhennet, Missy Ryan