At this very moment, Islamic State fighters backed by tanks, are trying (and succeeding, its seems) in taking the northern Syrian border town of Kobani (aka Ayn-al-Arab). While the Turkish army looks on from the heights across the border, Kurdish militias are fighting a fierce gun battle in the eastern part of the town, while Allied airstrikes pound IS positions in the west.
Notably absent over the battlefield - at least to this civilian mind - is the A-10 "Warthog" Thunderbolt II. I doubt this plane needs any introduction. Designed to counter the waves of Soviet tanks expected to pour across Europe during the Cold War, it's one of the finest ground-attack aircraft ever to take flight.
It's been famously said that this was an aircraft designed around a gun, the famous 30mm GAU-8/A "Avenger" which can fire depelted uranium shells up to 3,900 rounds a minute. It can otherwise carry pretty much anything other US aircraft can carry, but much more of it. It's straight wing configuration gives it excellent lift, giving it excellent "low and slow" capabilities.
IS has several Soviet-era AAA including the Zu-23 but the "Warthog" is legendarily durable. In a memorable incident during the 2003 invasion of Iraq, an A-10 suffered significant damage from flak, but despite a damaged engine and loss of hydraulic power, the pilot landed safely.
Wikipedia reports that the USAF 124th Fighter Wing, which flies A-10's, will be re-basing, as scheduled, to the Middle East in September 2014. I wonder if anyone can confirm if this is the case, because I was starting to wonder why the USAF has not deployed these planes in the fight against IS.
Edit: Foxtrot Alpha is way ahead of me on this subject, obviously I missed this recent post.