A MILITARY BASE IN SOUTHWEST ASIA — As the Iraqi Security Forces and Kurdish Peshmerga fighters continue to close in on Mosul on the ground, the U.S. and coalition are saturating the air above them and to the west.

At any given time there are 15-20 aircraft right over Mosul to gather intelligence and to be in place for airstrikes. Most of those aircraft are unmanned and controlled from the Combined Air Operations Center (CAOC) at a military base in southwest Asia.

Inside the CAOC military officials stare at a series of screens with full motion video from drone feeds and at maps showing where aircraft are operating in the region.

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The drone feeds in the CAOC today displayed a range of subjects, from following a man as he loaded his vehicle, staying fixed on a compound, and even trailing a man speeding down a dirt road on a motorcycle.

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One screen shows what the U.S. military calls the "donuts" over Mosul — the concentration of aircraft essentially flying circles over the city to gather intelligence and potentially conduct strikes. With the operation to re-take Mosul entering the assault phase earlier this month, much of the surveillance is focused on that area, and there is now a specific surveillance mission focused on the area west of Mosul to the Syrian border.

The Iraqis approached Mosul from every direction except the west, leaving it open to give ISIS fighters "an avenue out," a U.S. military official said, adding, "the Iraqis do not want to 'rubblize' Mosul," or turn it into rubble with airstrikes.

ISIS fighters are using that avenue to escape the city — and then return to it. The U.S. military official said that ISIS fighters have been fleeing Mosul to take their families to Raqqa and Dayr az Zawr and then the men come back to Mosul to fight. The official said they are even seeing ISIS leaders kick Raqqa residents out of their homes to make way for the families of ISIS fighters who have fled the coming offensive in Mosul.

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While Mosul is the main focus now, the coalition also has a surveillance mission over Syria, particularly in the north. The U.S. military official characterized the air over northern Syria as “saturated” by surveillance aircraft for more than a year.

The general in charge of the air war over Iraq and Syria says that he is reviewing whether he has enough assets to cover the current mission and the eventual operation to re-take Raqqa.

Lieutenant General Jeff Harrigian said that additional air power could come from an aircraft carrier or he could “surge” aircraft to the area for a period of time. “We are already working through what it might take to bring in some more assets,” Harrigian said.