Photo: US Army

U.S. Marine Corps counter-battery fire was unable to destroy the location from which the rockets were launched, as ISIS is known to use mobile launchers and quickly abandon its fire location.

The Marines, who are from the 26th Marine Expeditionary Unit, are armed with 155m artillery weapons able to reach targets at distances greater than 30-kilometers. The weapons are designed to thwart and destroy any approaching ISIS forces hoping to advance upon massing Iraqi forces or launch attacks.

When it comes to the eventual full assault on Mosul, Warren did not deny that U.S. military firepower from "Firebase Bell" might support attacking Iraqi Security Forces with offensive artillery attacks, but did not confirm the possibility either – explaining he did not wish to elaborate on potential future operations.

Overall, there are roughly 3,700 U.S. troops in Iraq, however that number could rise by a thousand or two in coming weeks - depending upon how many U.S. forces are temporarily assigned to the region.