M61 Vulcan rotary cannon, the standard cannon in most U.S. combat aircraft since the 1960s, mounted on either an armored vehicle or a trailer.
The weapon is mounted on a modified M113 vehicle (the M741 carrier). The system was designed to complement the M48 Chaparral missile system. The M163 uses a small, range-only radar, the AN/VPS-2, and an M61 optical lead-calculating sight. The system is suitable for night operations with the use of AN/PVS series night vision sights that can be mounted to the right side of the primary sight.
The gun fires at 3,000 rounds per minute in short bursts of 10, 30, 60, or 100 rounds, or it can fire in continuous fire mode at a rate of 1,000 rounds per minute. A linkless feed system is used.
From the beginning, the main drawback of the M163 was its small caliber and lightweight shells, which limited its effective range. Early M50 series ammunition exacerbated the situation, but the M163 was still comparable to the contemporary Soviet ZSU-23-4; although the Russian ZSU fired a larger shell (23 mm rather than 20 mm) and a higher rate of fire, the M163 had a higher muzzle velocity providing a flatter trajectory, shorter time of flight and thus better accuracy.
Unlike the ZSU the M163 has no search radar, and has limited engagement capability against aircraft at night. The M163 gunner is exposed in the open turret, whereas in the ZSU-23-4 the gunner is in a fully enclosed armored turret; this gives the M163 gunner much better situational awareness and field of view at the cost of losing protection against rifle-caliber weapons. This is important, especially since the M163 has no search radar.
In US and Israeli service the VADS has rarely been needed in its intended purpose of providing defense against aerial threats—consequently the Vulcan gun system was in use throughout the late 1980s and early 1990s primarily as a ground support weapon. For example, VADS guns were used to support American ground assault troops in Panama in 1989 during Operation Just Cause. One Vulcan of B Battery, 2/62 ADA even sank a PDF Vosper PT boat. The last combat action the VADS participated in was Operation Desert Storm.