The U.S. Air Force is rebuilding tens of thousands of World War II-era cannon rounds specifically for the 40mm cannons on its AC-130U Spooky II. Though the service has long been looking to finally retire this particular part of the gunship’s arsenal, which has increasingly become a logistical nightmare, the aging guns have so far proven too effective to get rid of completely. In November 2017, the U.S. Air Force revealed that the 780th Test Systems Squadron at Eglin Air Force Base in Florida had been testing the upgraded 40mm high explosive ammunition, known as the PGU-9D/B, earlier in the year. The new version combines decades old components with a fuze that is safer and more reliable than the original model. Some of the brass cartridge cases had production date stamps dating to 1944.

In all, the service plans to rebuild approximately 80,000 older rounds into the new configuration. The 780th developed the process to modify the existing ammunition and build a number of prototype rounds, but it is unclear whether the unit, which handles various munitions testing duties, will perform the rest of the work or how long the process might take in total. Air Force Special Operations Command (AFSOC) controls all of the service’s AC-130 gunships, which include the Us, as well as newer AC-130W Stinger IIs and still in development AC-130J Ghostriders. The project does speak to the continued importance of both the AC-130U and its 40mm Bofors cannon. To give a sense of the demand for the aircraft, according to an official Air Force history, seven of the Spooky IIs assigned to the 4th Special Operations Squadron flew nearly 4,000 combat hours between November 2013 and June 2014. The planes and their crews spent more than 1,175 days deployed to conflict zones during that time.

USAF Members of the 780th Test Systems Squadron load a PGU-9D/B round into a test gun during testing.

In October 2017, members of the crew of one of the 4th's AC-130Us, which had gone by the callsign Spooky 43, received Distinguished Flying Crosses and other medals for valor for one particularly intense mission over Afghanistan in 2016. The gunship beat back insurgents who had ambushed a team of U.S. Army Special Forces personnel from three sides, having to fire both 40mm shells and rounds from the aircraft's larger 105mm howitzer dangerously close to friendly troops. At present, the Spooky II is the only system of any kind left in the U.S. military to use the weapon in any capacity. In addition to the PGU-9 rounds, gunners can fire high explosive-incendiary, armor-piercing shells, or a mixture of all three types, depending on the target set.

USAF An AC-130U Spooky II gunship.