BRUSSELS –One of the dozen AH-64 Apache helicopters that have been available to Iraqi combat units for months in their fight against Islamic State militants has destroyed an ISIS vehicle during a sortie over Iraq, Secretary of Defense Ash Carter said June 13.

More than one Apache flew in the strike that occurred in the past 24 hours, but only one fired a weapon at the ISIS vehicle, a senior Pentagon official told reporters. Neither Carter nor the official would elaborate on why the Apaches were tasked with the strike instead of a variety of aircraft already engaged in the campaign to degrade and destroy the terrorist organization.

The Apaches were deployed to Iraq specifically to support Iraqi military units in their efforts to envelop and recapture Mosul from ISIS.

“It is a capability that has been prepared and made available to the Iraqis for some time,” Carter told reporters during a flight to Brussels for a series of NATO ministerial meetings. “The reason I think its use was timely…why the Iraqi and U.S. commanders decided to use it, was because it could be effective at helping those forces that are positioning themselves for envelopment of Mosul.”

“We had long anticipated that would be the time it would be used,” Carter said of the Apaches based in Iraq.

Iraqi forces, with U.S. troops, artillery and aircraft in support, are preparing to encircle and lay siege to Mosul, a major ISIS operational base in Iraq. A pair of offensives–one from the north and another from the southeast and southwest, are converging on the city in a plan that has been five months in the making, Carter said.

Also ongoing is the fight to retake Fallujah, which Carter said is progressing as planned.