In a rural valley in southern Yemen lies Wadi Rafad, a collection of farms 50 miles from the provincial capital of Ataq. Amid an arid landscape dotted with lemon orchards and cornfields, villagers were used to the peace being disturbed by the buzzing of US drones flying overhead. But on the afternoon of May 6, 2012, something changed.

Around 4.30pm an aircraft came into view, its white fuselage clearly visible against the stark blue sky. Rather than overfly the valley, the CIA drone fired Hellfire missiles straight at Fahd al-Quso, who was working his land. He was killed instantly — but shrapnel from the blast also engulfed Nasser Salim Lakdim, a 19-year-old student who had just returned home to tend his family's plantation. Nasser's father came rushing back to the farm to find his son in pieces. "It was horrifying, I can barely describe it," he told VICE News.

The strike was among the foremost successes of the US counterterrorism effort in Yemen. Al-Quso, its target, was a senior field commander in al-Qaeda in the Arabian Peninsula (AQAP). He had participated in the bombing of the USS Cole in 2000 and had threatened to attack American embassies.

It was also an example of successful cooperation between British and American intelligence agencies. The US had hunted al-Quso for half a decade, and the intelligence that led to this strike came from a British agent working for the UK's Secret Intelligence Service (SIS) — commonly known as MI6 — who had infiltrated AQAP.

Far from being a one-off tip, a VICE News investigation can exclusively reveal that this was a high point in systemic collaboration between SIS and the CIA to degrade AQAP through a combination of special forces operations and drone strikes.

A former senior CIA official responsible for operations in Yemen told VICE News that "the most important contribution" to the intelligence for the strike came from "a very important British capability." The UK agent provided the CIA with al-Quso's position, allowing a drone to track his car. "That was quite unique," the former official explained, "it was something we didn't have."

The use of drones in Yemen has long been characterized as a unilateral US policy. In response to a 2014 parliamentary question on Britain's role in the US drone program, UK Minister of State for Foreign Affairs Hugh Robertson said: "Drone strikes against terrorist targets in Yemen are a matter for the Yemeni and US governments."

However, following interviews with more than two dozen current and former British, American, and Yemeni officials, VICE News can reveal that the UK played a crucial and sustained role with the CIA in finding and fixing targets, assessing the effect of strikes, and training Yemeni intelligence agencies to locate and identify targets for the US drone program. The US-led covert war in Yemen, now in its 15th year, has killed up to 1,651 people, including up to 261 civilians, according to The Bureau of Investigative Journalism.

"The involvement of the British state is something that the government ought to make plain to parliament," David Davis MP, chair of the UK's All-Party Parliamentary Group on drones, told VICE News. "If we know we're handing intelligence over which will be used in a killing then we ought to be confident that it meets our own rules and guidelines. If there are deaths of civilians there's a moral and legal problem."

Nasser was not the first unintended casualty in strikes targeting al-Quso. The strike on Rafad was the fourth attempt and collectively these killed 32 people. US military documents published by The Intercept in 2015 cite a sample study of strikes in Afghanistan where almost nine out of 10 people killed were never identified, casting doubt on the robustness of methods for establishing a positive identification of the target.

The Rise of AQAP

The Western counterterrorism effort in Yemen began in 2001. UK and US intelligence agencies identified al-Qaeda training camps in Osama bin Laden's ancestral homeland and US Central Command requested that the UK's Special Air Service (SAS) be on standby to conduct "stiletto" attacks — or precision raids — to destroy the camps. The following year, the CIA carried out its first drone strike against al-Qaeda in Yemen.

Yemeni President Ali Abdullah Saleh proved an enthusiastic ally, and most of al-Qaeda's leaders were soon killed or captured. Saleh expected to be rewarded with US help in defeating a rebellion by the Houthis; a political movement dominated by Zaydi Shia Muslims. Instead he got encouragements to introduce democracy and tackle corruption, while military aid was slashed.

Weeks after an angry Saleh returned from meetings in the US in 2006, two dozen al-Qaeda suspects escaped from a maximum-security prison in what Gregory Johnsen, an expert commentator on Yemen, described as AQAP's "genesis moment." In response, military aid was restored, and UK and US trainers were deployed to mentor Yemen's counterterrorism forces.

Britain sent two teams: a Maritime Training and Advisory Team of Royal Marines and Navy personnel, tasked with training Yemen's coastguard to tackle smuggling and piracy, and a Counterterrorism Training Advisory Team, initially made up of special forces, deployed to bolster Yemen's Central Security Forces (CSF), a paramilitary unit run by President Saleh's nephew, Colonel Yahya Saleh.

"It was the British who pushed the Americans to work with us," Colonel Saleh told VICE News. "They provided live ammunition training, ops preparation and information gathering. They helped to set up the Intelligence Fusion Center."

Operating in a dangerous environment, the trainers sought to maintain a low profile. Colonel Saleh described the UK trainers as highly secretive: "They stipulated that we couldn't take their photos, or mention their names; even when we were honoring the American trainers the British avoided having their names mentioned."

But the CSF faced major problems in operating outside Sanaa, the Yemeni capital. Khalid Ahmed al-Radhi, then a contractor with US special forces and a close ally of President Saleh, noted that "these special forces, they take years [to train], it is not something you can get in one year."

A former colleague describes the defense attaché as going 'totally native. He was chewing qat three or four days a week.'

Stephen Seche, US ambassador to Yemen between 2007 and 2010, said "it took an awful lot of work to get [Yemeni special forces] into a more effective counterterrorism force." Basic logistical issues and political rivalries hampered attempts to intercept al-Qaeda suspects. "That forced us to go back and reassess to what extent we put Yemeni forces out in front." In many cases, US special forces would take the lead.

British forces also, on occasion, took the lead. In Sanaa, the British training team was living in a team house, moved every six months for security reasons, with a permanent medic. However, according to UK military personnel who served in Yemen, some rooms were kept empty for "temporary visitors" — British special forces who were flown in for short missions. Due to the low profile maintained by the British trainers, these teams could avoid drawing attention.

Some "visitors" were described as taking part in "hits," or missions to kill-or-capture AQAP fixers and facilitators. "If they were coming to do a hit, they would come in, do their thing, and then disappear again," recalled one British soldier. But these methods could only be used close to Sanaa, and on a small scale. While operations to capture fixers were valuable for intelligence, they could not counter the growing threat posed by AQAP.

AQAP continued to expand both its membership and its capabilities. In 2007, the group added to its ranks Ibrahim al-Asiri who would earn a reputation as a master bomb maker after finding a foot soldier to trial his latest invention. This militant, Umar Farouk Abdulmutallab, attempted to detonate explosives in his briefs on Northwest Airlines Flight 253 above Detroit on Christmas Day 2009. The detonator failed, but al-Qaeda and the "Underwear Bomber" had almost claimed 290 lives.

US President Barack Obama then admitted that there had been a "systemic failure" of the nation's security apparatus. Under pressure to act, American security agencies flooded Yemen with intelligence resources. In January 2010, General David Petraeus, then the head of US Central Command responsible for Yemen, met President Saleh in Sanaa, who agreed that the Americans should deploy drones to help increase the precision of operations, following a devastating US cruise missile attack on a Bedouin encampment in al-Majala in 2009, when 45 civilians — including 12 women and 22 children — were killed.

The UK government also reacted with concern. Abdulmutallab had lived in Britain for three years while studying at University College London, where he was president of the Islamic Society. Prime Minister Gordon Brown promised an expansion of UK support to Yemen.

Underscoring the seriousness of the threat, al-Asiri was then implicated in the creation of two "undetectable" bombs placed on international cargo planes. Both bombs were intercepted on October 29, 2010 — one at the UK's East Midlands airport, the other in Dubai. Later that day, Sir John Sawers, chief of SIS, made his first-ever public speech in which he identified Yemen as one of three "real threats," concluding: "Our intelligence effort needs to go where the threat is."

The Hunt for Targets

Operating in Yemen presented innumerable challenges. Seche explained that the risks were often too high to operate in the field, adding: "I'm frustrated to this day that we lost opportunities, because I didn't want to call Washington and say we lost lives today."

Networks of human intelligence — sources on the ground — were therefore invaluable in locating targets, and this is where the British came in. "The defense attaché of the British embassy was much more active than the American. He was meeting with everybody," recalled al-Radhi. "If you know Yemen, people act differently when you chew qat [a stimulant plant] with them; they get used to you and they start opening up. The British got closer to people."

A former colleague describes the defense attaché as going "totally native. He was chewing qat three or four days a week. But the Yemenis loved him for it."

Seche explained: 'We had a targeting list with names that we could pursue'

The defense attaché was not involved in intelligence work, but he illustrates some of the skills that Britain brought to the counterterrorism effort. The SIS team in Yemen was by all accounts highly effective. "The British have been in Gulf states for decades. They have a reservoir of knowledge, contacts, and expertise that is very important," a former senior CIA official, responsible for operations in Yemen, explained. "If you look at what capabilities each side has, that starts to tell you something about precisely where the actionable intelligence is coming from."

One British official, working in an intelligence capacity, was more blunt: "Our station people were pretty shit-hot."

The Americans valued Britain's connections and networks of human intelligence, but the British also wanted to be involved in American operations to learn about potential threats to the UK. A former senior Yemeni diplomat said: "The British wanted to know every arcane detail because Britain had become a target. For that reason, Britain had to take part on an operational level... but they didn't want it to be known."

The operational level included drone strikes, for which British sources fed into the hunt for targets. Seche explained: "We had a targeting list with names that we could pursue." He described working with UK officers as, "very collaborative, and it was very useful for both [Britain and America] to sit and help triangulate what we were hearing from our different sources."

"If we are providing explicit intelligence to identify individuals who we know the Americans are going to go and kill by drone strike then that's a kill list," David Davis MP told VICE News.

'Our station people were pretty shit-hot'

Once SIS or the CIA had identified a target, they would collaborate on preparing a Target Package — outlining the actionable intelligence — and the CIA would request permission to strike from Ammar Saleh, deputy director at the Yemeni National Security Bureau (NSB), its principal intelligence agency.

Al-Radhi explained that the NSB would try to corroborate the intelligence: "The Americans would say we have a target. People from the NSB wouldn't give permission until they contacted their people on the ground and confirmed what the Americans said."

The British also played a key role here. US, UK, and Yemeni military and diplomatic sources confirmed that British personnel worked in a Joint Operations Room at the NSB, assisting in intelligence gathering. Ali al-Ahmadi, NSB director between 2012-2015, told VICE News that, "SIS co-operated with us a lot in mentoring our surveillance team, which prepares for raids and arrests, observation of targets, and fixing them. That was really one of the reasons for the success of the NSB."

Al-Ahmadi confirmed that UK mentoring was both "theoretical and operational" and that "the surveillance teams were a British specialism."

British personnel serving in Yemen confirmed that two of the trainers were operators from the Special Reconnaissance Regiment (a special forces unit), who had been seconded to SIS. This made their presence deniable by the UK Ministry of Defence (MoD), which said in a 2014 statement to human rights NGO Reprieve: "The UK does not provide any military support to the US campaign of Remotely Piloted Aircraft System (RPAS) strikes on Yemen."

The secondment allowed British military personnel to assist with the drone program, but under the aegis of intelligence operations managed by the FCO.

Three other trainers were SIS intelligence officers. In addition to the NSB they helped to train Yemen's Political Security Organization (PSO), the country's secret police, in surveillance, communications, and intelligence-gathering — all of which helped to establish positive identifications of targets before drone strikes. The PSO has been implicated in systemic human rights abuses.

Parallel to SIS efforts, British military trainers were responsible for training the Yemeni Counter Terrorism Unit (CTU), including setting up their surveillance section and an Intelligence Fusion Center, used to manage networks of sources and analyze intelligence gathered during hits on AQAP fixers. The CTU included a unit of women, who specialized in surveillance. CIA officers would visit the Fusion Center on a weekly basis to collect its product.

Just how many strikes occurred as a result of intelligence provided by SIS remains a closely guarded secret. However, British human intelligence, including the agent who provided the information leading to the strike on al-Quso, played a prominent role in the hunt for the master bomb maker al-Asiri. In this they collaborated closely with Saudi Arabia.

'Surveillance teams were a British specialism'

Mustafa Alani, a director at the Gulf Research Institute, who has close ties to the Saudi Interior Ministry, told VICE News that the SIS agent involved in the strike that killed al-Quso was also crucial in eight additional missions. He was "able to help electronic identification of the targets," said Alani, allowing SIS and the CIA to match cell phones and other electronic devices to names on the list of targets. "None of these operations could be successful without that."

The usual process, as Abubakr al-Qirbi — Yemen's foreign minister between 2000 and 2014 — explained, was that the British would help with "tracking and informants would say that Mr. X is moving from one place to the other. They would pass it to the Americans and the American drone would try to follow the target."

A former senior CIA official would not confirm the number but conceded that the same SIS agent was involved in multiple strikes. VICE News has established that civilians were killed in at least two of these strikes; one of which targeted al-Quso.

The second strike, based on intelligence provided by the same British agent, killed a doctor who is referred to in GCHQ documents leaked by Edward Snowden as "Khalid Usama... who pioneered using surgically implanted explosives." A disciple of al-Asiri, the target was believed to be part of a concerted AQAP effort to develop an explosive that could be placed inside a human body and walked onto aircraft without alerting security.

That strike took place on March 30, 2012. A Reaper fired three Hellfire missiles at a car that it had been tracking, killing the AQAP surgeon and a fellow militant, as well as a civilian bystander — 60-year-old Saleh Muhammed Saleh al-Sunna — and injuring six children.

Nabeel Khoury, US deputy chief of mission in Sanaa from 2004 to 2007, wrote in 2013 that, "Drone strikes take out a few bad guys to be sure, but they also kill a large number of innocent civilians. Given Yemen's tribal structure, the US generates roughly 40 to 60 new enemies for every AQAP operative killed by drones."

David Davis concurred: "Killing people from a clear sky who are guilty of nothing is a very fast way of signing up a lot of people to our enemies."

Jennifer Gibson, staff attorney at human rights NGO Reprieve, which represents the family of Nasser Salim, killed in the strike targeting al-Quso, said: "For years, the British government has denied any involvement in the US's covert drone war in Yemen, saying it's 'a matter for the states involved.' It's now beyond dispute the UK is one of those states — working hand in glove with the Americans to create the very kill list that drives those strikes. Even more disturbing, the UK has copied wholesale the US model of outsourcing the military to the intelligence agencies in order to hide their involvement and avoid any accountability."

Protesters in Sanaa burn an effigy of a US aircraft during a demonstration against interference in Yemen. (Photo by Khaled Abdullah/Reuters)

Internal Disagreements

In 2011 — one year into the escalated drone offensive — Yemen was thrown into turmoil by the Arab Spring, weakening Saleh's 34-year grip on power. With demonstrations in Sanaa, British military trainers were withdrawn. Although SIS remained active, and the drone campaign continued, the disintegration of central control allowed AQAP to wrest control of Abyan and Shabwa provinces from government forces.

Under pressure from the US and UK, President Saleh agreed to hand over the reins to his deputy, Abd Rabbuh Mansur Hadi, on condition that he could stay in Yemen. When President Hadi was sworn into office in February 2012 Yemen was riven by internal political feuding in the face of an expanding jihadist insurgency and a poverty rate of 54.5 percent. Desperate to regain full control Hadi gave permission for over 100 US Navy, Marines, and Army personnel to set up in al-Anad airbase. Whereas Saleh had told General Petraeus that "you must stay in the joint operations room... out of sight," Hadi gave the US more freedom to engage AQAP openly.

The effect was immediate. In 2012 alone the US launched almost twice as many special operations attacks in Yemen as they had over the previous decade. Abubakr al-Qirbi — who served as foreign minister under both Hadi and Saleh — accused Hadi of giving the US and UK a "blank check."

The security crisis also prompted the relaxation of the rules of engagement. Seche, by then back in Washington, explained that "there was a sense that AQAP was metastasizing and therefore we should broaden the target base and move down into mid-level operatives."

The subsequent targeting process of "signature striking" proved to be the most controversial aspect of the drone program. Rather than hitting identified targets, US drones began to fire on unidentified groups engaging in "suspicious" activity, arising from observed patterns of behavior — or signatures — by military-aged males. Former US, British, and Yemeni officials all told VICE News that these strikes targeted AQAPs moneymen, couriers, and fixers.

Seche commented that this "made us all very uneasy... it is hard to corroborate... and it is very risky because you can get into miscalculations and really get into civilian casualties."

On August 29, 2012, a CIA drone fired on five men sitting by a car at the edge of Khashamir village in eastern Yemen. One was a local policeman. Another, Salem bin Ali Jaber, was a local preacher who regularly denounced al-Qaeda in his sermons. The other three were unknown to locals.

For the British these strikes were unacceptable. Michael Stephens, a Middle East research fellow at the Royal United Service Institute, told VICE News that, "our rules of engagement are tighter than the US, and I would say these very difficult interpretations of what constitutes a combatant and what doesn't are where we can find a disagreement with the Americans. Our involvement is very much in an intelligence supporting role."

As a result of the shift in tactics, British military personnel were informed that they could no longer collaborate with the US on intelligence sharing. According to a British official familiar with the program, when military trainers returned to Yemen in early 2012, they were told that "all the routine intelligence sharing... we couldn't do because of the drone program and our requirement for counterterrorism rule of law."

Once again they were working with Yemen's CSF, but were reduced to four personnel and a liaison from the FCO counterterrorism team. Rather than working from a team house, they were billeted in the Sheraton Hotel in Sanaa, were not allowed to join Yemeni forces in the field, and were banned from carrying weapons.

However these rules did not apply to SIS, who are overseen by the FCO, or to special forces seconded to SIS. The strike targeting al-Quso occurred after the shift to signature striking, and SIS continued to find and fix targets for the drone program throughout this period, according to British, American and Yemeni officials**.** British special forces operators also continued to mentor Yemen's intelligence agencies.

A British official noted that, "once they are seconded, the MoD loses any control over what they get up to." This allowed the MoD to remain in compliance with the European Convention on Human Rights, while British troops were nonetheless used to assist in the assassination of targets.

Dr. Emile Nakhleh, a former senior officer in the CIA who set up the agency's Political Islam Center and testified before Congress on the Underwear Bomber, emphasized that the UK and US had "disagreements over procedures rather than strategic objectives" and that "the UK's role has been pretty critical" in the counterterrorism campaign in Yemen.

Body bags of the five men killed by a CIA drone strike in Khashamir, including an anti-AQAP imam and policeman. (Photo by Faisal bin Ali Jaber via Reprieve)

By 2014, however, those strategic objectives were thrown into confusion by the unraveling of the Yemeni state. Unimpressed by the reforms proposed by President Hadi, the Houthis rebelled once more, and with the counterterrorism effort focused on al-Qaeda made rapid gains. Military trainers were withdrawn. By September, Sanaa fell and the government was exiled, first to Aden, then out of the country as the Houthis continued to push south. In the confusion, AQAP expanded its territory, taking over al-Mukalla, a major provincial capital.

Saleh too made a comeback, allying with the Houthis to regain a grip on Sanaa. Expressing his frustration at events, Seche said the "idea [had been] to provide economic support to allow Hadi to strengthen his position... We should have seen that Saleh was just going to use that as an opportunity to come in here and throw a monkey wrench into everything we were trying to do."

With the withdrawal of the embassies and collapse of governmental structures, many of the networks of human intelligence fell away, and in early 2015 US special forces abandoned their listening post at al-Anad airbase. The US drone program is still active, made easier by AQAP holding identified territory. British intelligence sharing also continues, said Ali al-Ahmadi, former head of the NSB.

However Britain has failed to persuade Saudi Arabia, which intervened at the head of a coalition of Gulf States in Yemen in March 2015, to target AQAP. The coalition air campaign has principally targeted the Houthis and forces loyal to Ali Abdullah Saleh. The bombing campaign has devastated towns and cities, and led to a humanitarian crisis.

Even when the drone campaign was at its peak intelligence capacity, mistakes were common. Numerous strikes targeting AQAP leaders actually hit unidentified individuals and the criteria for establishing a positive identification were shown to be far from watertight. In the absence of human intelligence, capabilities are greatly reduced. Meanwhile the laws surrounding the sharing and use of intelligence by allied governments are entirely opaque.

Responding to the VICE News' investigation, an FCO spokesperson said: "We have previously provided counter-terrorism capacity building support to the Yemeni security services to increase their ability to disrupt, detain, and prosecute suspected terrorists in line with Yemeni rule of law and international human rights standards. Following the closure of the Embassy in Sanaa in February 2015 we suspended this activity. We continue to work with regional and international partners to tackle the threat posed by terrorist organizations including AQAP and Daesh-Yemen [using an alternative acronym for the Islamic State group] and to build regional capacity on counterterrorism."

An MoD spokesperson said: "The MoD does not comment on special forces operations, or intelligence matters."

British MP Harriet Harman — chair of the UK's Joint Parliamentary Committee on Human Rights — emphasized the need to clarify the rules for intelligence sharing. "We must look at governance where we hand intelligence to others, such as the US, leading to a strike," she told an audience at the Royal United Service Institute conference on drones in November 2015. "We are culpable in that process."

Follow Namir Shabibi on Twitter: @nshabibi

Follow Jack Watling on Twitter: @Jack_Watling