The U.S. Marine Corps are taking their "instant gunship" with them when they go to Afghanistan this years. Called Harvest Hawk, it's a KC-130J tanker that is transformed into a gunship with some temporary additions.
The U.S. Marine Corps wants gunships, having noted the success of the U.S. Air Force AC-130 aircraft. But they can't afford them, as an AC-130 costs more than three times as much an a marine KC-130J aerial refueling aircraft. But the marines have a solution.
The KC-130J is the latest, and largest, USMC version of the C-130 transport used for aerial refueling. But the KC-130J can also carry cargo, and weapons (bombs and missiles) hung from the wings. Thus the Harvest Hawk version of the KC-130J adds a targeting pod, with the data going to a special cargo container containing control equipment (computers, commo and displays) enabling operators use of the day/night sensors of the targeting pod, to fire Hellfire missiles hung from the wings. A 30mm Bushmaster cannon is fired out the door, so that there would be gunfire support as well.
The Mk44 30mm Bushmaster cannon weighs 344 pounds and fires at 200 or 400 rounds per minute (up to 7 per second). The cannon has 160 rounds available, before needing a reload. That means the gunner has 25-50 seconds worth of ammo, depending on rate of fire used. Each 30mm round weighs about 25 ounces (depending on type.) Explosive anti-personnel rounds are fired when used in gunships. The fire control system and night vision sensors, enable the 30mm gunners to accurately hit targets with high explosive shells.
Existing AC-130 gunships are armed with a 105mm howitzer, a 25mm and 40mm automatic cannon. But these guns are being phased out of military service. The air force is considering equipping its gunships with smart bombs and missiles.