This undated image posted online on Aug. 31 by supporters of the Islamic State shows Abu Muhammad al-Adnani, the group’s spokesman and chief strategist, who was killed in a U.S. airstrike. (AP)

For a man given to fiery rhetoric and long-winded sermons, Abu Muhammad al-Adnani became oddly quiet during his last summer as the chief spokesman for the Islamic State.

The Syrian who exhorted thousands of young Muslims to don suicide belts appeared increasingly obsessed with his own safety, U.S. officials say. He banished cellphones, shunned large meetings and avoided going outdoors in the daytime. He began sleeping in crowded tenements in a northern Syrian town called al-Bab, betting on the presence of young children to shield him from the drones prowling the skies overhead.

But in late August, when a string of military defeats suffered by the Islamic State compelled Adnani to briefly leave his hiding place, the Americans were waiting for him. A joint surveillance operation by the CIA and the Pentagon tracked the 39-year-old as he left his al-Bab sanctuary and climbed into a car with a companion. They were headed north on a rural highway a few miles from town when a Hellfire missile struck the vehicle, killing both of them.

The Aug. 30 missile strike was the culmination of a months-long mission targeting one of the Islamic State’s most prominent — and, U.S. officials say, most dangerous — senior leaders. The Obama administration has said little publicly about the strike, other than to rebut Russia’s claims that one of its own warplanes dropped the bomb that ended Adnani’s life.

But while key operational details of the Adnani strike remain secret, U.S. officials are speaking more openly about what they describe as an increasingly successful campaign to track and kill the Islamic State’s senior commanders, including Adnani, the No. 2 leader and the biggest prize so far. At least six high-level Islamic State officials have died in U.S. airstrikes in the past four months, along with dozens of deputies and brigadiers, all but erasing entire branches of the group’s leadership chart.

The Islamic State said one of its longest-serving and most prominent leaders, Abu Muhammad al-Adnani, has been killed in Syria. (Reuters)

[Iraqi fighters facing brutal tactics from Islamic State’s Mosul defenders]

Their deaths have left the group’s chieftain, Abu Bakr al-Baghdadi, increasingly isolated, deprived of his most capable lieutenants and limited in his ability to communicate with his embattled followers, U.S. officials say. Baghdadi has not made a public appearance in more than two years and released only a single audiotape — suggesting that the Islamic State’s figurehead is now in “deep, deep hiding,” said Brett McGurk, the Obama administration’s special envoy to the global coalition seeking to destroy Baghdadi’s self-proclaimed caliphate.

“He is in deep hiding because we have eliminated nearly all of his deputies,” McGurk said at a meeting of coalition partners in Berlin this month. “We had their network mapped. If you look at all of his deputies and who he was relying on, they’re all gone.”

The loss of senior leaders does not mean that the Islamic State is about to collapse. U.S. officials and terrorism experts caution that the group’s decentralized structure and sprawling network of regional affiliates ensure that it would survive even the loss of Baghdadi himself. But they say the deaths point to the growing sophistication of a targeted killing campaign built by the CIA and the Defense Department over the past two years for the purpose of flushing out individual leaders who are working hard to stay hidden.

[‘I thought, this is it’: One man’s harrowing escape from the Islamic State]

The effort is being aided, U.S. officials say, by new technology as well as new allies, including deserters and defectors who are shedding light on how the terrorists travel and communicate. At the same time, territorial losses and military defeats are forcing the group’s remaining leaders to take greater risks, traveling by car and communicating by cellphones and computers instead of couriers, the officials and analysts said.

“The bad guys have to communicate electronically because they have lost control of the roads,” said a veteran U.S. counterterrorism official who works closely with U.S. and Middle Eastern forces and who, like others interviewed for this article, spoke on the condition of anonymity to discuss sensitive operations. “Meanwhile our penetration is better because ISIS’s situation is getting more desperate and they are no longer vetting recruits,” the official said, using a common acronym for the terrorist group.

This image made from video posted on a militant website on July 5, 2014, shows the leader of the Islamic State, Abu Bakr al-Baghdadi, delivering a sermon at a mosque in Iraq during his first public appearance. (AP)

“We have a better picture inside ISIS now,” he said, “than we ever did against al-Qaeda in Iraq.”

The caliphate’s cheerleader

The first to go was “Abu Omar the Chechen.” The red-bearded Georgian Islamic militant, commonly known as Omar al-Shishani, fought in the Russia-Georgia war in 2008 and had been trained by U.S. Special Forces when he was in the Georgian military. He rose to become the Islamic State’s “minister of war” and was reported to have been killed on at least a half-dozen occasions since 2014, only to surface, apparently unharmed, to lead military campaigns in Iraq and Syria.

Shishani’s luck ran out on July 10 when a U.S. missile struck a gathering of militant leaders near the Iraqi city of Mosul. It was the beginning of a string of successful operations targeting key leaders of the Islamic State’s military, propaganda and “external operations” divisions, U.S. officials said in interviews.

On Sept. 6, a coalition airstrike killed Wa’il Adil Hasan Salman al-Fayad, the Islamic State’s “minister of information,” near Raqqa, Syria. On Sept. 30, a U.S. attack killed deputy military commander Abu Jannat, the top officer in charge of Mosul’s defenses and one of 13 senior Islamic State officials in Mosul who were killed in advance of the U.S.-assisted offensive to retake the city.

On Nov. 12, a U.S. missile targeted Abd al-Basit al-Iraqi, an Iraqi national described as the leader of the Islamic State’s Middle Eastern external-operations network, responsible for carrying out attacks against Western targets.

But it was Adnani’s death that delivered the single biggest blow, U.S. analysts say. The Syrian-born Islamist militant was regarded by experts as more than a mere spokesman. A longtime member of the Islamic State’s inner circle, he was a gifted propagandist and strategic thinker who played a role in many of the organization’s greatest successes, from its commandeering of social media to its most spectacular terrorist attacks overseas, including in Paris and Brussels.

[These images show how Islamic State dug in for a ferocious defense of Mosul]

His importance within the organization was also steadily rising. Last year, after the U.S.-led coalition began retaking cities across Iraq and Syria, it was Adnani who stepped into the role of cheerleader in chief, posting messages and sermons to boost morale while calling on sympathetic Muslims around the world to carry out terrorist attacks using any means available.

“He was the voice of the caliphate when its caliph was largely silent,” said Will McCants, an expert on militant extremism at the Brookings Institution and author of “The ISIS Apocalypse,” a 2015 book on the Islamic State. “He was the one who called for a war on the West.”

The CIA and the Pentagon declined to comment on their specific roles in the Adnani operation. But other officials familiar with the effort said the task of finding the Islamic State’s No. 2 leader became a priority nearly on par with the search for Baghdadi. But like his boss, Adnani, a survivor of earlier wars between U.S. forces and Sunni insurgents in Iraq, proved to be remarkably skilled at keeping himself out of the path of U.S. missiles.

“His personal security was particularly good,” said the U.S. counterterrorism official involved in coordinating U.S. and Middle Eastern military efforts. “And as time went on, it got even better.”

But the quality of the intelligence coming from the region was improving as well. A U.S. official familiar with the campaign described a two-stage learning process: In the early months, the bombing campaign focused on the most visible targets, such as weapons depots and oil refineries. But by the middle of last year, analysts were sorting through torrents of data on the movements of individual leaders.

The information came from a growing network of human informants as well as from technological innovations, including improved surveillance drones and special manned aircraft equipped with the Pentagon’s Enhanced Medium Altitude Reconnaissance and Surveillance System, or EMARSS, designed to identify and track individual targets on the ground.

“In the first year, the strikes were mostly against structures,” said a U.S. official familiar with the air campaign. “In the last year, they became much more targeted, leading to more successes.”

Watching and waiting

And yet, insights into the whereabouts of the top two leaders — Baghdadi and Adnani — remained sparse. After the Obama administration put a $5 million bounty on him, Adnani became increasingly cautious, U.S. officials say, avoiding not only cellphones but also buildings with satellite dishes. He used couriers to pass messages and stayed away from large gatherings.

Eventually, his role shifted to coordinating the defense of a string of towns and villages near the Turkish border. One of these was Manbij, a Syrian hub and transit point for Islamic State fighters traveling to and from Turkey. Another was Dabiq, a small burg mentioned in Islam’s prophetic texts as the future site of the end-times battle between the forces of good and evil.

Adnani picked for his headquarters the small town of al-Bab, about 30 miles northeast of Aleppo. There he hid in plain sight amid ordinary Syrians, conducting meetings in the same crowded apartment buildings where he slept. As was his custom, he used couriers to deliver messages — until suddenly it became nearly impossible to do so.

On Aug. 12, a U.S.-backed army of Syrian rebels captured Manbij in the first of a series of crushing defeats for the Islamic State along the Turkish frontier. Thousands of troops began massing for assaults on the key border town of Jarabulus, as well as Dabiq, just over 20 miles from Adnani’s base.

[How the Islamic State has turned into a catastrophe for Sunni Muslims]

With many roads blocked by hostile forces, communication with front-line fighters became difficult. Adnani was compelled to venture from his sanctuary for meetings, and when he did so on Aug. 30, the CIA’s trackers finally had the clear shot they had been waiting for weeks to take.

Records generated by commercially available aircraft-tracking radar show a small plane flying multiple loops that day over a country road just northwest of al-Bab. The plane gave no call sign, generally an indication that it is a military aircraft on a clandestine mission. The profile and flight pattern were similar to ones generated in the past for the Pentagon’s EMARSS-equipped MC-12 prop planes, used for surveillance of targets on the ground.

The country road is the same one on which Adnani was traveling when a Hellfire missile hit his car, killing him and his companion.

The death was announced the same day by the Islamic State, in a bulletin mourning the loss of a leader who was “martyred while surveying the operations to repel the military campaigns against Aleppo.” But in Washington, the impact of his death was muted by a two-week delay as U.S. officials sought proof that it was indeed Adnani’s body that was pulled from the wreckage of the car.

The confirmation finally came Sept. 12 in a Pentagon statement asserting that a “U.S. precision airstrike” targeting Adnani had eliminated the terrorist group’s “chief propagandist, recruiter and architect of external terrorist operations.”

The Russian claims have persisted, exasperating the American analysts who know how long and difficult the search had been. Meanwhile, the ultimate impact of Adnani’s death is still being assessed.

Longtime terrorism experts argue that a diffuse, highly decentralized terrorist network such as the Islamic State tends to bounce back quickly from the loss of a leader, even one as prominent as Adnani. “Decapitation is one arm of a greater strategy, but it cannot defeat a terrorist group by itself,” said Bruce Hoffman, director of Georgetown University’s Center for Security Studies and an author of multiple books on terrorism. Noting that the Islamic State’s military prowess derives from the “more anonymous Saddamist military officers” who make up the group’s professional core, Hoffman said the loss of a chief propagandist was likely to be “only a temporary derailment.”

Yet, as still more missiles find their targets, the Islamic State is inevitably losing its ability to command and inspire its embattled forces, other terrorism experts said. “The steady destruction of the leadership of the Islamic State, plus the loss of territory, is eroding the group’s appeal and potency,” said Bruce Riedel, a 30-year CIA veteran and a terrorism expert at the Brookings Institution. “The Islamic State is facing a serious crisis.”

Thomas Gibbons-Neff contributed to this report.

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