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: this 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.
General Dynamics / Raytheon Phalanx Close-In Weapon System
Error creating thumbnail: File missingPhalanx Block 1 CIWS - 20x102mmError creating thumbnail: File missingPhalanx Block 1A CIWS - 20x102mm. The Block 1A has a new electronic system which allow it to integrate with other weapons systems aboard ship, as well as introducing a barrel restraint to increase accuracy.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 powered mounting 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; the cylinder houses the system's tracking radar, while the dome houses the search radar. A land-based version called the Centurion Counter-Rocket, Artillery, Mortar (C-RAM) has also been developed, and is used to protect point bases against rocket attacks. Rather than using the tungsten armour-piercing discarding sabot rounds of the naval version, the land-based version uses High-Explosive Incendiary Tracer, Self-Destruct [HEIT-SD] ammunition, which was originally designed for the M163 VADS self-propelled anti-air system. 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.
