VIETNAMIZATION THIS TIME (profanity alert):

The battle of Mosul began officially on Oct. 17, 2016. Sonically, it didn't come into its own until some weeks later. In the opening skirmishes, as Iraqi troops encountered Islamic State fighters on farmland and in villages outside the city, rounds whistled unobstructed through the air and thudded in the sod, a vague overture. When the troops breached the easternmost districts of the city proper -- in early November -- then you could begin to really listen to the conflict.

On an evening later that month, I was embedded with a company of Iraqi Special Operations Forces in a neighborhood near Mosul's eastern edge from which they had expelled the jihadists. The troops had set up a temporary command post and barracks in a group of commandeered homes surrounding a plaza that included a mosque and a park, or what had been a park -- now it was a mud patch where Humvees, armored bulldozers and a fuel tanker were parked. Most of the modest rowhouses in this neighborhood -- Zahra, a middle-­class enclave of shopkeepers and pharmacists and taxi drivers -- had made it out of the fighting intact; others were crumpled but salvageable; others were mere rubble. The sunset was threaded through with black smoke from the car fires ISIS had lit to try to obscure its positions from aerial surveillance. The futility of this tactic could be heard and felt every few minutes, as a jet dove in to drop a bomb, or a heavy artillery shell found its target, with an atmosphere-­consuming shriek and a thunderous, belly-­seizing impact. And yet ISIS set the cars ablaze every day.

After dark, a polyphony of firefights broke out around our position. The reliable chatter of rifles, the more insistent clangor of machine guns, the congested peals of rocket-­propelled grenades went back and forth. The airstrikes and artillery continued. At midnight, I climbed to a roof, ducked below the parapet -- ISIS snipers had night-­vision equipment, it was believed, though they were good enough not to need it -- and peered over. Mosul is situated in a riverine basin, so that a high enough spot can give you a view over the city's ancient marble walls, the domes and minarets of its medieval mosques, the balconies of its cinder block apartment houses. The car fires had created around the city a necklace of Boschian throbbing orange-­red.

A sinister chorale crept into the gunfire -- ISIS fighters baying from mosque loudspeakers. "Allahu akbar! Allahu akbar!" Others shouted the phrase in the streets. From more loudspeakers came an ISIS anthem. I asked a soldier how the same song could come from different places in unison. He pulled from his fatigues a pocket radio and tuned it to 92.5 FM.

"ISIS's radio station," he said.

At the time, Zahra and a few areas around it represented a minute but expanding peninsula of military occupation jutting into the city, whose 251 neighborhoods were otherwise entirely controlled by ISIS. The plan was to push the jihadists west toward the Tigris River, which bisects Mosul, then encircle them on the west side. No one knew how many fighters were waiting. Some soldiers estimated a thousand, some five times that. Some believed that the battle would take two months, others a year. However many fighters there were, ISIS knew they were not enough to face off in the streets with the Iraqi forces pouring into Mosul: roughly 10,000 troops, with an additional 90,000 militiamen, police officers and Kurdish soldiers massed on the city's perimeter. Flying above Mosul were the jets, bombers, helicopters and unmanned aerial vehicles of an American-­led international coalition, and around it was a constellation of heavy artillery firebases.

So ISIS, in its efforts to hold Mosul -- or, really, to kill as many people and destroy as much of the city as it could while losing it, as the jihadists knew they inevitably must -- relied on tactics known in Western military parlance as "harassing fire." It was a phrase that amused Iraqi soldiers whose English was sufficient to understand its insufficiency and who had to actually endure this harassment. ISIS's harassers included world-class snipers, crack mortar teams, the suicidal drivers of vehicle-­borne improvised explosive devices, or V.B.I.E.D.s -- mobile car bombs -- and, to direct these efforts, something new to warfare, a fleet of commercial-­market drones. ISIS managed to smuggle untold numbers of the small, cheap machines, the kind of thing you can buy on Amazon, into Mosul.

On his phone, a sergeant major showed me a video taken by one of the enemy drones, which the jihadists used to target strikes as well as record them. When a strike was successful, they would quickly edit the video and put it online, part of the steady diet of near-real-time footage that each side supplied the internet. The troops watched ISIS's videos as avidly as everyone else -- another of this battle's weird techno-­wrinkles. This particular clip, uploaded a few days earlier, showed a car bomber speeding up a street not far from where we were now, toward a group of parked Humvees. "Those are ours," said the sergeant major, Karim. The car bomber slammed into a Humvee. A ghostly gray expanded in the middle of the screen. "I was injured," Karim said, lifting up his shirt to reveal a scar. "No, wait. This is from something else."

It was hard to keep track. The Iraqi special forces had been fighting ISIS for more than two years. They had fought them near Baghdad, in Ramadi, then Falluja, Tikrit and Baiji, pushing the jihadists north nearly 250 miles to Mosul, the caliphate's greatest urban stronghold. Many of Karim's comrades had fought Al Qaeda and ISIS's other precursors before that. The tip of the spear into Mosul, the special forces had been going without a break for weeks now, taking heavy casualties. Karim had been wounded five times since Ramadi. In Falluja, a rocket skivered a Humvee in which he was the gunner. It was the scar from that attack that he wanted to show me, a discolored sunken patch below his rib cage. Looking down at it, he said, "It was a big hole before."

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