Lt. Jamal Derwish, the outpost’s commander, said his men already spotted three such armored vehicles in the area since Islamic State, or ISIS, overran the city of Ramadi last month and seized yet another arsenal of modern U.S.-made heavy weapons from the Iraqi army. Islamic State fighters, he said, have also filled trenches with oil to burn—something that would create a smokescreen to protect them from U.S. airstrikes…

The 160,000 Peshmerga—the troops of the autonomous Kurdish regional government in northern Iraq—may well be the most dedicated and combat-worthy units confronting Islamic State in Iraq. In a paradox of this conflict, they are also the least armed and equipped when compared with the Iraqi army, the Iranian-backed Shiite militias or, crucially, Islamic State itself. Peshmerga ammunition stocks are running low and whatever heavy weapons they have are mostly of Saddam Hussein-era vintage, commanders say.

While the Peshmerga also buckled under Islamic State’s rapid offensive last summer, they have since reconquered most lost territory and now are focused on holding the line. One of the most critical front lines is here near the Islamic State stronghold of Hawija, in the barren hill country punctuated by the burning gas wells of Kirkuk province. The area is home to a sizable chunk of the country’s oil wealth.

“If ISIS combines its forces and pushes into one area with multiple vehicles, they will break through—and then the whole line breaks,” warned Wladimir van Wilgenburg, a Kurdistan-based analyst for the Jamestown Foundation, a Washington think tank.