Assad’s government has killed almost seven hundred medical personnel. Illustration by Brian Stauffer

On a recent Tuesday evening in London, the surgeon David Nott attended a dinner at Bluebird, an upscale Chelsea restaurant. The room was packed with doctors, renowned specialists who had come for the annual consultants’ dinner of the Chelsea and Westminster Hospital, one of Britain’s leading medical establishments. As waiters set down plates of lamb and risotto, Nott checked his phone and found a series of text messages. “Hi David,” it began. “This is an urgent consultation from inside Syria.” Attached was a photograph of a man who had been shot in the throat and the stomach.

The image had been sent by a young medical worker in Aleppo. He had removed several bullets from the patient’s small intestine, but he wasn’t sure what to do about the wound in the throat. For the past hour, the man had been slowly dying on the operating table while the medical worker awaited instructions.

“Sorry, didn’t see your message till now,” Nott typed under the table. “Is the neurology ok?” It was: a bullet had pierced the trachea and the esophagus, but it hadn’t damaged the spinal cord. Nott told the medical worker to insert a plastic tube into the bullet hole, to provide an even supply of air. Then, he instructed, sew up the digestive tract with a strong suture, and, “to buttress the repair,” partly detach one of the neck muscles and use it to cover the wound.

Nott returned to his lamb, which had gone cold. There were around fifty specialists in the room—many more than there are in the opposition-controlled half of Aleppo, where, in 2013 and 2014, Nott had trained medical students, residents, and general surgeons to carry out trauma surgeries far beyond their qualifications. Several had since been killed, and Nott often checked in with the others, especially when he saw reports that Syrian or Russian aircraft had attacked hospitals around the city.

In the past five years, the Syrian government has assassinated, bombed, and tortured to death almost seven hundred medical personnel, according to Physicians for Human Rights, an organization that documents attacks on medical care in war zones. (Non-state actors, including ISIS, have killed twenty-seven.) Recent headlines announced the death of the last pediatrician in Aleppo, the last cardiologist in Hama. A United Nations commission concluded that “government forces deliberately target medical personnel to gain military advantage,” denying treatment to wounded fighters and civilians “as a matter of policy.”

Thousands of physicians once worked in Aleppo, formerly Syria’s most populous city, but the assault has resulted in an exodus of ninety-five per cent of them to neighboring countries and to Europe. Across Syria, millions of civilians have no access to care for chronic illnesses, and the health ministry routinely prevents U.N. convoys from delivering medicines and surgical supplies to besieged areas. In meetings, the U.N. Security Council “strongly condemns” such violations of international humanitarian law. In practice, however, four of its five permanent members support coalitions that attack hospitals in Syria, Yemen, and Sudan. The conditions in Syria have led to a growing sense among medical workers in other conflict zones that they, too, may be targeted.

Despite the onslaught, doctors and international N.G.O.s have forged an elaborate network of underground hospitals throughout Syria. They have installed cameras in intensive-care units, so that doctors abroad can monitor patients by Skype and direct technicians to administer proper treatment. In besieged areas, they have adapted hospitals to run on fuel from animal waste. Nott, for his part, trained almost every trauma surgeon on the opposition side of Aleppo, as part of a daring effort to spread medical knowledge as the government strives to eradicate it.

As a child, Nott constructed hundreds of model airplanes from kits and from scratch, and hung them from the ceiling of his bedroom, in Worcester. His dream was to fly commercial jets, and in secondary school he earned his pilot’s license. But his father, an Indo-Burmese surgeon who had married a British nurse, wanted him to become a doctor. “He used to sit there in my room, forcing me to learn,” Nott told me when I visited him at his private clinic in London, last month. Nott, who is fifty-nine, speaks softly, and has a calm, professorial demeanor. In 1978, he enrolled in the medical program at Manchester University, where he marvelled at human anatomy. “The most exciting machine is a human being,” he said. “It’s actually the same as an airplane or a helicopter. They both have an engine. They both require fuel.”

Shortly before Christmas in 1993, Nott was working as a general surgeon at Charing Cross Hospital, in London, when he saw a television report from Sarajevo. For twenty months, the city had been under siege by the Bosnian Serb Army, and the program showed a field hospital in need of staff. The next day, Nott volunteered with Médecins Sans Frontières, and on Christmas Eve he left for a three-month stay in Sarajevo, where he worked at a facility that had been so severely damaged by shelling and sniper fire that people called it Swiss Cheese Hospital.

After that trip, Nott took long periods of unpaid leave from his jobs at various London hospitals to volunteer for humanitarian-aid agencies in other areas afflicted by war and natural disaster. He operated on thousands of patients in more than twenty countries—including Afghanistan, Sierra Leone, Haiti, and Nepal—often with rudimentary equipment and insufficient supplies of medication and donor blood. The conditions forced him to learn an array of surgical techniques that in London would all have been carried out by different specialists.

In 2008, on the day that Nott arrived at an M.S.F. hospital in Rutshuru, in the Democratic Republic of the Congo, he found a sixteen-year-old orphan whose arm had been improperly amputated. The stump was infected, and the muscles were gangrenous. Without a forequarter amputation—a complicated procedure in which the entire shoulder is removed, usually as a last resort to halt the spread of cancer—the boy would die. Nott had never done the operation, so he sent a text message to Meirion Thomas, who was Lead Surgeon at the Royal Marsden Hospital, in London. Minutes later, Thomas replied, “Start on clavicle. Remove middle third.” He sent nine more steps, and signed off, “Easy!” The boy recovered.

At the time, military doctors in Iraq and Afghanistan were adopting a transformative approach to the worst battlefield-trauma cases. Typically, surgeons treated life-threatening abdominal bleeds from gunshots and bomb blasts by cutting open the abdomen, searching for the damaged organs and arteries, repairing them, and stitching up the incisions. The fixes could take hours, and patients often died on the operating table after their body temperature plummeted.

American and British military surgeons started practicing “damage-control surgery,” an established concept that hadn’t been applied in combat zones. Practitioners do the absolute minimum to stop the bleeding and prevent sepsis before sending patients to the intensive-care unit for warming, fluids, and resuscitation. The patient returns to the operating theatre only when his body is stable enough to handle hours under the knife.

“I wanted to be a part of this surgical revolution,” Nott told me. “And the only way to do that is actually to be there, to get the case in front of you. You can’t read it in a book.” He volunteered as a surgeon with the Royal Air Force and was quickly deployed to Basra, in Iraq, and later to Camp Bastion, in Afghanistan. At Camp Bastion, in 2010, “we had a thousand and seventeen major trauma cases in six weeks,” he recalled. “It was people with their arms and legs blown off. It was people shot in the head, people shot in the chest, people with fragmentation injuries everywhere.” Two years later, Queen Elizabeth II awarded Nott the title of Officer of the Order of the British Empire for his medical work in war zones.