The US M163 20mm Vulcan Air Defence System is a converted M113 APC and mounted with a 20mm Vulcan mini-gun. 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. In the M163 a linkless feed system is used, in the M167 (towed) linked ammunition is used.
In 1984 the improved PIVADS (Product-Improved VADS) system was introduced, providing improvements in the ease of use and accuracy of fire, but the limitations of the 20x102mm calibre remained. Eventually the M48 and M163 were both replaced in US service by the M1097 Avenger and the M6 Linebacker (M2 Bradley with FIM-92 Stinger missiles instead of the standard TOW anti-tank missiles): the Stinger missile providing the necessary range to deal with helicopters with anti-tank missiles far outranging the 20mm gun, as well as considerably extending the reach against fixed-wing targets.
In US and Israeli service the VADS has rarely been needed in its intended purpose of providing defence against aerial threats – consequently the Vulcan gun system was in use throughout the late 80’s and early 90’s primarily as a ground support weapon.