Six months ago, Sunni Arab militants faced a daunting firepower imbalance in their uprising against the U.S.-equipped Iraqi army west of Baghdad.

But once their campaign for the city of Fallouja was launched in January, their lethal capabilities were bolstered from the stockpiles of the Iraqi armed forces.

Many soldiers fled, throwing down their weapons, which were picked up by the insurgents. Police stations and security posts overrun by Sunni militants yielded more martial booty to be turned against the forces of Prime Minister Nouri Maliki’s Shiite Muslim-led government. […]