Joint Chiefs Chairman Army Gen. Martin Dempsey summed up the recent victory by Islamic State militants in the key Iraqi city of Ramadi this way:

"The [Iraqi security force] was not driven out of Ramadi; they drove out of Ramadi."

Technically, Dempsey was accurate. The Iraqi army abandoned its last remaining positions in Ramadi on Sunday after a chaotic battle that involved a dust storm, dozens of Islamic State car bomb attacks and a breakdown in communications between the beleaguered Iraqi troops on the ground and the American advisers who can provide them with air support, according to U.S. officials.

Officials this week are offering new details of the four-day battle that, in the end, saw the Islamic State, also known as ISIS, raising its black flag over the capital building of Anbar province and declaring its most significant victory in nearly a year.

It began with that dust storm, which enabled militants to launch a wave of suicide bomb attacks at a moment when the city streets were shrouded in orange haze.

Iraqi troops had limited visibility and feared their American ally's capability to provide air cover might be compromised. The initial attack targeted Ramadi's governing center, where the Iraqi army maintained a heavily fortified headquarters.

"There was an armored bulldozer which knocked over the T-wall perimeters, which then was the first explosion. They then had an armored dump truck, an armored Humvee," one senior State Department official said in describing the initial attack.

That was the first in a series of about 30 car bombs, about 10 of which packed "the explosive capacity of an Oklahoma City-type attack," the State Department official said, referring to the 1995 domestic terrorist attack on a federal office building that killed 168 people.

"They took out entire city blocks," said the official, who briefed reporters on condition of anonymity.

Morale among the besieged Iraqi army forces already was low. Those units had been deployed to Ramadi for a year with no leave, no pay over the past six months and no proper resupplies, according to an NBC News report that cited U.S. officials.

The Iraqis also had limited ability to reach back and communicate with their higher headquarters. That confusion led to the ground forces' mistaken belief that "because [of the dust storm], they would not be able to receive air power support," Army Col. Steve Warren, a Pentagon spokesman, said Thursday.

"The weather did not impact our ability to conduct airstrikes. But we are coming to the understanding that the commander on the ground believed otherwise," Warren said.

Theoretically, the Iraqi ground troops should be in constant radio contact with their rear echelon and Iraq's combined joint operations center, where American officers are standing by to receive requests for air support and respond immediately.

But that's not how it worked during this battle. "It's unclear at this point what the communication links were at the time," Warren said.

On Sunday, the Iraqi army tried to send a "reinforcing column" into Ramadi's city center, but those troops immediately came under fire and retreated, "which then began a broader retreat from where the security forces were holding," the State Department official said.

The final decision to abandon Ramadi did not come from Iraqi headquarters, Warren noted. "This appears to be a unilateral decision made by a commander on the ground, an Iraqi commander on the ground in Ramadi, based on his assessment of the situation that it was time to withdraw," he said.

In an interview with the Wall Street Journal, Dempsey suggested that the Iraqi decision to leave was deliberate and did not reflect a defeat in direct combat. That interview was where Dempsey observed that the Iraqi troops were "not driven out of Ramadi, they drove out of Ramadi."

A prominent Iraqi author, Hisham al-Hashimi, offered a more pointed analysis on Twitter: "Corrupt [Iraqi security forces] commanders in Ramadi took bribes in exchange for battle plans and logistical information."

The fleeing Iraqi army units left behind millions of dollars of American-made military gear, including "dozens" of tracked vehicles, among them about half a dozen M1 Abrams tanks and about 100 armored Humvees and other vehicles, U.S. military officials said.

About 3,000 U.S. troops are deployed to Iraq, most advising and training Iraqi forces inside secure military installations. U.S. officials repeatedly have said they believe the strategy to defeat ISIS is working and no major changes are needed.

Still, officials acknowledge the loss of Ramadi as a significant victory for ISIS and its attempt to expand its so-called caliphate.

"They see their entire campaign as a war of flags, expanding the flags, and so that's why this is very important," the State Department official said.

But U.S. officials also hope the setback is temporary and say this defeat looks nothing like the ISIS advance last June. When militants seized Mosul, Iraqi army units fled in droves and ISIS consolidated control over dozens of cities in northern Iraq.

"We all remember the experience from Mosul, where you just had a domino collapse," the State Department official said.

The official said Ramadi "remains a very serious situation," but added: "I think the silver lining here is ... that the lines more or less have held. You don't have, again, a Mosul situation of a collapse."