The Americans, too, have had to learn fast; many of them are part of this summer’s influx of troops and, like Colonel Voorhees’s men, have been in the field for only a month or two. One of the companies in his task force lost two men, who were killed by an improvised bomb in Mehlajat, but otherwise casualties have been slight: five Afghan police officers, wounded by another bomb.

Now the Afghan police and American troops are settling in to create a permanent presence in this quarter of Kandahar City. Many of the 200 Afghan policemen are fresh recruits, straight from a six-week training program; 10 to 20 percent have not even been issued rifles yet, one of their own commanders said and American officers confirmed.

“They get a police baton and that’s all,” said Police Col. Abdul Qadim. “Can you imagine coming here with a stick?”

The Americans bring an array of modern weaponry, from surveillance drones to close air support. “We have to backstop them at every stage,” Colonel Voorhees said. “But they are out in front.”

The Americans also bring a greater appreciation for Afghan sensibilities than in the past. Lt. David Thompson brought along a backpack stuffed with $45,000 in Afghanis, the national currency, and spent $20,000 of that in three days — paying on-the-spot reparations to residents whose homes or fields were damaged in the fighting.

The operation in Mehlajat has three companies of American troops hunkered down in the fields and orchards, patrolling on foot. The Afghans are patrolling on foot with them, and even sleeping in the open.

Colonel Qadim is the head of what will become the new Police Substation 15, which at the moment consists of a semicircular trench with an orchard wall at its back and fields of corn and okra in front of it. While the Afghans took a break at sunset to eat their iftar meal on Monday, marking the end of the day’s fasting for Ramadan, Americans took up prone positions atop the ditch’s berm, pulling security for them.