“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 UN convoys from delivering medicines and surgical supplies to besieged areas.

In meetings, the UN 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 NGOs 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 MSF 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.

In the first weeks of March, 2011, the start of the insurrection in Syria, the security forces of President Bashar al-Assad detained and tortured children who had drawn anti-regime slogans on a wall in the southern city of Dara’a. Tens of thousands of protesters took to the streets, and on March 22nd Assad’s forces stormed into the city hospital, kicked out the nonessential medical staff, and positioned snipers on the roof. Early the next morning, the snipers fired at protesters. A cardiologist named Ali al-Mahameed was shot in the head and the chest as he tried to reach the wounded. Thousands of people attended his funeral, later that day, and they, too, were attacked with live ammunition. For the next two years, the snipers remained stationed on the roof, “firing on sick and wounded persons attempting to approach the hospital entrance,” according to the U.N. commission.

As protests erupted all over the country, government-run hospitals basically functioned as an extension of the security apparatus, targeting demonstrators who dared to seek treatment. “Some doctors manage to treat simple cases and manage to let them flee without being seen or registered,” one doctor said, in testimony collected by Médecins Sans Frontières. “But if an admission is required for the patient, then the administration of the hospital is notified, and therefore it reaches security.”

Pro-regime medical staff routinely performed amputations for minor injuries, as a form of punishment. Many wounded protesters were taken from the wards by security and intelligence agents, sometimes while under anesthesia. Others didn’t make it as far as the hospital; security agents commandeered ambulances and took the patients straight to intelligence branches, where they were interrogated and often tortured and killed. M.S.F. concluded that, for Syrians who opposed the President, the health-care system was “a weapon of persecution.”

In response, some doctors established secret medical units to treat people injured in the crackdown. One surgeon at Aleppo University Hospital adopted the code name Dr. White. Along with three colleagues, he identified and stocked safe houses where emergency operations could be performed. Dr. White also lectured at the university’s faculty of medicine; he suspected that seven of his most promising students shared his sympathies toward the nascent uprising. Another doctor, named Noor, recruited them to join the mission. In Arabic, noor means “light,” so the group called itself Light of Life.

At night, Noor and Dr. White gave the medical students lessons via Skype, concealing their faces and voices. The goal was to teach them the principles of emergency first aid, with an emphasis on halting the bleeding from gunshot wounds. During demonstrations, the students waited in cars and vans to shuttle injured protesters to the safe houses, then disappeared. “They had to leave the house before my arrival,” Dr. White told me during a recent Skype call from Aleppo. “They could not know who this man is.”

Similar covert medical networks sprouted up all over Syria. But the safe houses were equipped with little more than gauze, cotton, and serum. One doctor told M.S.F., “When we receive serious casualties—a patient who needs to be hospitalized—we have two options: either we let him die or we send him to hospital not knowing what will become of him.”

In the first year of the uprising, Physicians for Human Rights documented fifty-six cases of medical workers being targeted by government snipers; tortured to death in detention facilities; shot and set on fire while driving ambulances; and murdered by security agents at checkpoints, in their clinics, or at home. Several were killed while treating patients. In July, 2012, the regime enacted a new terrorism law, making it an offense to fail to report anti-government activity; according to the U.N. commission, this “effectively criminalized medical aid to the opposition.”

That summer, Noor, the founder of Light of Life, was kidnapped at his clinic by security agents and later killed. Three of Dr. White’s students were also abducted; their charred corpses were found the following week. “From that day, I changed my name another time,” he told me. “I became Abdul Aziz”—the name he uses today