During ISIS's blitz across northern and central Iraq last month, the group captured upwards of 52 155mm M198 howitzers.

These U.S.-supplied artillery pieces have a range of up to 20 miles and can also be outfitted with GPS aiming systems. The howitzers' range could place Baghdad, as well as many other major Iraqi cities, squarely within bombardment range of ISIS. 

Jeremy Binnie, an analyst for British military consultancy HIS Janes, told McClatchy DC that he doubted the Islamists would be able to learn how to use the GPS aiming systems quickly. However, the weapons can fire two rounds a minute and could still cause considerable damage to cities through imprecise fire.