The U.S. Air Force is buying 16 C-130J transports, for $100 million each for conversion into AC-130J gunships. Equipping the new gunships will nearly double the price, and the first one won't enter service until 2017. These will replace older AC-130H gunships. The air force will keep 17 more recent (1990s) AC-130Us. The AC-130U has an additional 25mm autocannon and the ability to track more than one target at a time.
The AC-130H gunship (nicknamed Spooky) is a 69 ton, 4 engine aircraft, armed with two 20mm machine-guns, a 40mm autocannon, and a 105mm howitzer. While the aircraft can stay in the air for 6 hours (or more, if it refuels in the air), what really makes a difference is how well the weapons operate. Flying low (often under 3,000 meters/10,000 feet) and at night, the gunship relies on night vision devices and well trained gunners to take out targets that are giving the troops on the ground a hard time. Four decades of continuous improvements have made the gunships increasingly lethal. The AC-130J will be able to operate at 6,000 meters (above most ground fire) because it has missiles and SDB. This means it can operate in daylight, which gunships traditionally did not due because of the vulnerability to ground fire.
The 79 ton C-130J has a top speed of 644 kilometers, 40 percent more range than the C130H, and can carry 25 percent more cargo. The C-130J transport proved to be more than just another model in the 50 year old C-130 design. Mainly because it's cheaper and easier to use. Like most new commercial transports, the C-130 emphasizes saving money. The new engines generate 29 percent more thrust while using 15 percent less fuel. Increased automation reduced crew size from 4 to 3. The C-130J is more reliable and easier to maintain.
As a stopgap, to replace the elderly (and less often available for service) AC-130Hs that must retire, the air force has put into service 14 MC-130W "Dragon Spear" gunships. These are C-130Js temporarily outfitted with sensors and missiles and no cannon. These are proving quite useful and their “instant gunship” capability will probably be retained even after the AC-130Js replace all the AC-130Hs.