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
"Praise God, we soon had enough weapons to fight for one or two years," said Ahmad Dabaash, spokesman for the Islamic Army, a Sunni rebel faction, who spoke in a hotel lobby here in Iraq's northern Kurdistan region. "And now? Don't even ask!"
By "now," he was referring to the current ground assault by the
As the Iraqi government mobilizes to halt the insurgents' advance toward Baghdad, the capital, there is no full accounting of the stocks of plundered arms, ordnance and gear. But experts agree that the haul is massive, with implications for the merging wars in Iraq and neighboring Syria.
Rival Syrian rebel factions already report seeing U.S.-built, ISIS-commandeered Humvees almost as far west as the vicinity of Aleppo, some 250 miles from Iraq. The influx of arms and fighters from Iraq could shift the balance of power among fractious groups fighting for supremacy in Syria.
ISIS, which also reportedly snatched the equivalent of close to $500 million in cash from a Mosul bank, has been catapulted to the position of the world's wealthiest and best-equipped militant group, analysts say. Its riches easily eclipse those of Al Qaeda under Osama bin Laden, despite his personal fortune. The group, which has attracted thousands of fighters from the Arab world, Europe and elsewhere, also holds sway over a broad swath of contiguous territory in the heart of the Middle East.
"ISIS are well-trained, very capable, and have advanced weapons systems that they know how to use," said Michael Stephens, researcher at the Royal United Services Institute for Defense and Security Studies.
In the current ISIS-led thrust, the scenario played out earlier by Sunni insurgents in western Iraq has been replicated on a monumental scale.
Government forces retreated en masse from the onslaught, leaving behind a military hardware bonanza, including the U.S.-made armored Humvees as well as trucks, rockets, artillery pieces, rifles, ammunition, even a helicopter. Some of the seized materiel was old or otherwise non-functioning; but a lot was promptly put to use on the battlefield.
Pictures of grinning Islamist warriors cruising in U.S. Humvees bedecked with white-on-black militant flags flooded the Internet and became the signature image of the ISIS rampage.
ISIS social-media enthusiasts even mocked the global #BringBackOurGirls Twitter campaign, referring to girls kidnapped by an Al Qaeda offshoot in Nigeria. ISIS sympathizers began tweeting #BringBackOurHumvee.
Though ISIS initially encountered little opposition from the Iraqi army in central and western Iraq, the insurgents have not directly challenged Kurdish troops known as the peshmerga who control a more than 600-mile front in northern Iraq.
Stretching from the Syrian to Iranian borders, this territory is protected by the semiautonomous Kurdistan Regional Government. Iraqi soldiers who once patrolled much of the line retreated and are now found only along about a 35-mile stretch close to Iran, according to Kurdish security officials.
ISIS "took the weapons stores of the 2nd and 3rd [Iraqi army] divisions in Mosul, the 4th division in Salah al Din, the 12th division in the areas near Kirkuk, and another division in Diyala," said Jabbar Yawar, secretary-general of the Ministry of Peshmerga Affairs, punctuating his words with quick flicks of his laser pointer as he stitched a scythe-like arc across a map denoting various provinces and cities strung across northern and central Iraq.
"We're talking about armaments for 200,000 soldiers, all from the Americans," concluded Yawar, a mustachioed figure whose office in Irbil features a photograph of him as a young peshmerga fighter in the 1980s against the government of former Iraqi strongman Saddam Hussein.
With such an immense quantity of captured weaponry, Yawar said, ISIS and its confederates are now capable of laying down "a colossal intensity of bullets" against their foes.
Though the group's advance in Iraq has garnered headlines, the plundered weapons and a likely flood of new recruits might also shift the initiative among militant groups in neighboring Syria. ISIS emerged from the turmoil of the Syrian conflict but later suffered setbacks in internecine combat.
This year ISIS faced an assault from rival insurgent factions that cut its presence to a few strongholds in northern and eastern Syria, including the city of Raqqah. Various Syrian militant groups, including the Islamic Front and Al Nusra Front, the latter the official Al Qaeda franchise in Syria, are avowed enemies of ISIS, which broke away last year in a bitter dispute.
But the newly galvanized ISIS recently made substantial gains along the desert borderlands of the Iraqi-Syrian frontier. It seized the border town of Qaim and tore down border fences and bulldozed berms and ditches in a dramatic gesture meant to illustrate its goal of creating a unified Islamist caliphate.
ISIS forces also advanced near the eastern Syrian city of Dair Alzour, capital of the oil-rich province of the same name.
The lightning assault and attendant publicity may be winning new allies, even among Al Nusra Front.
Several days ago, a group of Al Nusra militants in the Syrian town of Bokamal, along the Euphrates River on the border with Iraq, pledged allegiance to ISIS, according to various accounts. ISIS's captured Humvees helped alter the balance of power on the border battlefield, said one Al Nusra fighter reached via Skype.
More ISIS militants and weapons are expected to pour into Syria from Iraq, said Col. Abdulrazzaq Abu Bilal, a commander with Al Tawheed Brigade, one of the Syrian groups arrayed against ISIS.
For a week, ISIS has been massing forces north of Aleppo and clashing with rival militant groups just 12 miles from the main highway linking Aleppo with Turkey, Bilal said in an interview via Skype from Syria.
"After the Iraqi borders opened and ISIS seized control of the Dair Alzour suburbs, this gave them the motivation to advance toward Aleppo," said Bilal, a defector from the Syrian air force.
The group's success has prompted President Obama to seek $500 million from Congress to train "appropriately vetted elements of the moderate Syrian opposition."
As ISIS continues to storm through Iraq, Bilal said, its leaders seem determined to repeat the same offensive trajectory in Syria — and regain areas ceded to rivals in northern Syria.
"They are seeking to control the Turkish border in its entirety," he said, and "to cut off the supply routes and retake all the areas they lost."