In June 1946, the General Electric Company was awarded the contract for "Project Vulcan." Rather than focusing on hitting power as European designers were doing with their slow-firing 30mm aircraft cannons, the project focused on a pre-war .60 caliber (15mm) anti-tank rifle cartridge, aiming for a rate of fire no less than 6,000 rounds per minute. The early T45 model using the .60 caliber round had issues with insufficient damage, and alternatives in 20mm and 27mm were tested, the T171 and T150 guns. In 1956 the T171 20mm gun was standardized by the US Army and US Air Force as the M61 20mm Vulcan aircraft gun.
The M61 Vulcan is an externally powered six-barrel rotary gun having a rate of fire of up to 7,200 rounds per minute. The firing rate is selectable at 4,000 or 6,000 rounds per minute. Each of the gun's six barrels fires only once during each revolution of the barrel cluster. The six rotating barrels contribute to long weapon life by minimizing barrel erosion and heat generation. The gun's rate of fire, essentially 100 rounds per second, gives the pilot a shot density that will enable a "kill" when fired in one-second bursts. The gun fires electrically primed 20x102mm ammunition and usually uses a hydraulic motor for power, though there is a self-powered version, the GAU-4 (M130 in Army service) which was used in the SUU-23/A / M25 gunpod. This variant uses an electric motor to spin up the barrel cluster, then sustains itself via gas operation.
While the initial M61 was troubled by issues with misfeeds and FOD damage to aircraft mounting it due to using linked ammunition, the linkless M61A1 Vulcan cannon is a proven gun, having been the US military's close-in weapon of choice dating back to 1959 when it was first fielded on the F-104C. The F-104, F-105, X-32, F-14, later models of the F-106, F-111, F-4, B-47, B-52 (until the 1990s) and B-58 all used the M61, as do the Air Force's F-15, F-16 and F-22, and the Navy's F/A-18. The primary use of the cannon is in the extremely short range (less than 2,000 feet) air-to-air environment, where more sophisticated air-to-air missiles are ineffective. Alternately, the cannon has limited usefulness in a ground strafing role.
While originally manufactured by General Electric, it is no longer produced by them; GE Armament Systems was sold to Martin Marietta; after their merger with Lockheed, it was produced by Lockheed Martin Armament Systems, which was bought by General Dynamics in 1997.
The M61 Vulcan Cannons used in the film industry have been converted to percussion primer cases using a sub caliber cartridge adapter.
Error creating thumbnail: File missingM167A2 VADS (Vulcan Air Defence System) - 20x102mm HEIT-SD. This is the towed variant; the VADS version mounted on the M113 APC is M163. This can be distinguished as an A2 Product Improved VADS (PIVADS) by having two wheels on each side: the A2 update also made improvements to the fire control and targeting systems.
The Vulcan Air Defense System (VADS) was a ground-based anti-aircraft version of the M61A1 developed to replace the obsolete WW2-era M45 Quadmount in the 1960s after the cancellation of the overly ambitious MIM-46 Mauler SAM system in 1965, with the towed M167 VADS entering service in 1967. The M113-mounted self-propelled version, the M163 VADS, entered service in 1969, replacing the M42 Duster. The two systems used a round developed specifically for them, the M246 High-Explosive Incendiary Tracer, Self-Destruct (HEIT-SD). As a point of trivia, the cancellation of Mauler and its naval variant also led to the adoption of the RIM-7 Sea Sparrow by the US Navy (which had been anticipating the navalized Sea Mauler and had already designed the Knox-class frigates around it) and the development of the British Rapier SAM system.
The VADS is a powered mounting which is manually aimed by the gunner with the radar only a rangefinder, and has an effective range of about three quarters of a mile against airborne targets and 1.25 miles against ground targets. The gun is electrically operated, using the vehicle's power supply for the M163 and either a generator or its own integral APU for the M167.
VADS (and its missile companion, the AIM-9 Sidewinder-based MIM-72 Chaparral) was always intended to be a stop-gap system, and was considered obsolete by the late 70s since Soviet attack helicopters were carrying the AT-6 Spiral with a range almost five times greater than it. However, due to the failure of the DIVADS program (which created the infamous M247 Sergeant York using the completely unsuited-for-task radar suite of an F-16, directing ancient and poorly-maintained Bofors 40mm cannon barrels left over from retired M42 Dusters in a 20-ton turret on a not-at-all-happy-about-this M48A5 Patton chassis) it was not directly replaced until 1994 when the AN/TWQ-1 Avenger entered service, though by this point the man-portable FIM-92 Stinger had largely replaced it operationally. The PIVADS (Product Improved Vulcan Air Defense System) program in 1984 upgraded stocks of M163s to the M163A2 standard and M167s to the M167A2 standard (it is not clear what A1 did for either system) with improvements to the fire control system and an extra wheel added on either side of the M167 to prevent rollovers while being towed.
General Dynamics / Raytheon Phalanx Close-In Weapon System
Error creating thumbnail: File missingPhalanx Block 1 CIWS - 20x102mm. Block 1 was a mostly internal upgrade to the original Block 0 system, improving most aspects of the system and increasing its maximum elevation to +70 degrees to deal with the threat of sea-skimming missiles that "pop up" in their terminal phase.Error creating thumbnail: File missingPhalanx Block 1 baseline 2 / Block 1A CIWS - 20x102mm. The Block 1A had a new electronic system which allowed it to integrate with other weapons systems aboard ship. The barrel restraint to increase accuracy was added by the Block 1 baseline 2 upgrade.Error creating thumbnail: File missingPhalanx Block 1B CIWS - 20x102mm. This is the current version which has a set of Optimised Gun Barrels (OGB) to increase accuracy and longevity, and Forward Looking Infra-Red (FLIR) which enable the CIWS to engage targets with a low radar observability and surface targets.Centurion C-RAM - 20x102mm. This is a land-based version of the Phalanx Block 1B CIWS mounted on a mobile trailer.
This is a self-contained powered mounting developed in the 1970s and first mounted to a combat vessel, the aircraft carrier USS Coral Sea, in 1980. It is used mostly by naval vessels to engage incoming missiles, aircraft, and sea-based close-range targets. It features a distinctive white-painted cylindrical weapon control group with a domed radome at the top which results in the nickname "R2-D2" being applied to the mounting (sometimes with a crude addition related to the position of the gun: some early reliability issues with Phalanx also led to sailors muttering that CIWS meant "Captain, It Won't Shoot!"); the cylinder houses the system's tracking radar, while the dome houses the search radar.
The original Phalanx Block 0 has been through a number of upgrades over the years. The Block 1 upgrade in 1988 was a general improvement to the installation's systems to deal with shortcomings of the Block 0 installation and the threat of new Russian supersonic anti-ship missiles: it included replacements for both radars, corrosion-resistant barrels, a higher maximum elevation and a larger magazine. The weapon also switched to using preloaded magazines and altered the magazine mounting to reduce reloading time from 20-30 minutes to less than 5. Two sub-upgrades, Block 1 baselines 1 (1989) and 2 (1995), respectively switched the gun from a hydraulic to a pneumatic drive system (increasing the rate of fire from 3,000 to 4,500 rpm and decreasing the half-second spin-up to almost zero) and added a barrel restraint to improve accuracy. Block 1A (1997) was primarily a systems update, adding a new high-order language computing system better able to engage manoeuvring targets, and allowing for integration with the US Navy's Ship Self Defense System, allowing the Phalanx's radar to be used to target the RIM-116 Rolling Airframe Missile. Block 1B was tested in 1999 and first mounted on the frigate USS Taylor (FFG-50) in 2000. This broad upgrade increases the system's traversing speed, adds a FLIR (forward-looking infrared) and video tracker on the left side of the weapon control group to increase the Phalanx's previously mediocre effectiveness against surface targets, alters the barrel restraint, and features lengthened (L/99 instead of L/76) Optimized Gun Barrels (OGB) for improved performance. The Block 1B mounting was also the basis of the later SEA RAM system, which replaces the Vulcan with an 11-tube RIM-116 Rolling Airframe Missile launcher.
A land-based derivative of Phalanx Block 1B called the Centurion Counter-Rocket, Artillery and Mortar (C-RAM) was first deployed in 2005 following a request from the US Army in 2004, and is used to protect point bases against rocket and mortar attacks. Rather than using the tungsten armour-piercing discarding sabot rounds of the naval version (aside from the original Mark 149 projectile, which was depleted uranium), the land-based version uses High-Explosive Incendiary Tracer, Self-Destruct (HEIT-SD) ammunition, which was originally designed for the VADS. More recently the C-RAM has been adapted to mount on a HEMMT truck meaning that it is fully mobile and self sufficient as opposed to the original C-RAM which was on a demountable towed trailer.
As a terminology note, Phalanx is an installation, not a turret, since it is mounted on the outside of a vehicle's hull rather than crossing it.
