Advisers are “combat multipliers.” Small teams of them vastly improve the performance of local troops, at a sliver of the cost of deploying large American battalions. Perhaps because of the divisive legacy of “adviser teams,” who were the first large-scale American commitment in Vietnam, it took years for the Pentagon to recognize this fact. Instead we poured hundreds of thousands of troops and billions of dollars into Iraq and Afghanistan year after year. The “surge” in 2007 worked precisely because it partnered Americans with Iraqi soldiers and tribes.

In 2006, I joined an adviser team in Habbaniya, halfway between Falluja and Ramadi, where the 450 Americans are headed. Our rotating group of 13 advisers lived on a remote outpost with 500 Iraqi soldiers, patrolling side by side. Even then, it took us three hard years to mold the battalion.

In 2005 and 2006, insurgents were shooting from houses where children were sleeping and blowing up themselves and dozens of bystanders in the market. No locals informed on the insurgents in their midst. Only by insisting on daily combat patrols were the advisers able to persuade the Iraqi soldiers that they could win the fight. We shared the risk; adviser casualties were over 30 percent.

The other key was being partnered with an American battalion, in our case Marine Battalion 3/2. The Iraqis gradually took pride in their own performance, mimicking the cocky Marines and their relentless advisers. In 2007, the people sensed the shifting advantage, the informant network swelled, and our Iraqi battalion, convinced that it should dominate the battlefield, destroyed the guerrilla network.

By 2008, Habbaniya had returned to its peaceful existence as a lakeside retreat. We were proud of the battalion, which became part of Iraq’s first independent brigade. But we were unnerved by President George W. Bush’s pledge to withdraw all American troops by 2011, with no plan for a residual force to watch over the army we had worked so hard to build. Senior military officials were mostly silent.