Aegis combat system

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The Aegis combat system is an integrated missile guidance system used by the United States Navy.

By the late 1960s, the U.S. Navy recognized that reaction time, firepower, and operational availability in all environments did not match the anti-ship missile threat. As a result, an operational requirement for an Advanced Surface Missile System (ASMS) was promulgated and a comprehensive engineering development program was initiated to meet that requirement. ASMS was re-named "Aegis" in December 1969 after the aegis, the shield of the Greek god Zeus.

The name is sometimes spelled AEGIS, supposedly an acronym for phrases such as "Advanced Electronic Guidance Information System." However, such attributions seem to be backronyms or fake etymologies. (It is also possible there has been some confusion with the EGIS software used by some AWACS aircraft.) The main manufacturer of the Aegis combat system, Lockheed Martin, makes no mention of it being an acronym.

The heart of the system is an advanced, automatic detect-and-track, multi-function three-dimensional phased array radar, the AN/SPY-1 (now up to the AN/SPY-1D version). Known as "the Shield of the Fleet," the Aegis high-powered (four megawatt) radar is able to perform search, tracking, and missile guidance functions simultaneously with a track capacity of over 200 targets at more than 200 miles. The first Engineering Development Model (EDM-1) was installed in the test ship, USS Norton Sound, in 1973. The Aegis system still requires the AN/SPG-62 radar for terminal guidance of Standard missles. This means that the maximum number of targets that can be engaged simultaneously are four for the Ticonderoga class and three for the Arleigh Burke class. [1]

The computer-based command-and-decision element is the core of the Aegis combat system. This interface makes the Aegis combat system capable of simultaneous operation against a multi-mission threat: anti-air, anti-surface and anti-submarine warfare. The Aegis system is being enhanced to act in a Theater Missile Defense role, to counter short- and medium-range ballistic missiles of the variety typically employed by rogue states (see Aegis Ballistic Missile Defense System).

The Navy built the first Aegis-equipped cruisers using the hull and machinery designs of Spruance-class destroyers. The first cruiser of this class was the Ticonderoga, which uses two twin-armed Mark-26 missile launchers, fore and aft. The commissioning of the sixth ship of the class, the Bunker Hill opened a new era in surface warfare as the first Aegis ship outfitted with the Martin-Marietta Mark-41 Vertical Launching System (VLS), allowing a wider missile selection, more firepower, and survivability. The improved AN/SPY-1B radar went to sea in the Princeton, ushering in another advance in Aegis capabilities. The Chosin introduced the AN/UYK-43/44 computers, which provide increased processing capabilities.

In 1980, a destroyer was designed using an improved sea-keeping hull form, reduced infrared, and radar cross-section and upgrades to the Aegis Combat System. The first ship of the Arleigh Burke class, the USS Arleigh Burke, was commissioned in 1991. Because the Aegis system dominates the ship's architecture, ships equipped with it are sometimes mistakenly called Aegis class ships.

Flight II of the Arleigh Burke class, introduced in 1992, incorporates improvements to the SPY radar, and to the standard missile, active electronic countermeasures, and communications. Flight IIA, introduced in 1994, added a helicopter hangar with one anti-submarine helicopter and one armed attack helicopter. The Aegis program has also projected reducing the cost of each Flight IIA ship by at least $30 million.

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Iran Air Flight 655

The Aegis system was involved in an incident in which USS Vincennes mistakenly shot down Iran Air Flight 655 in 1988 resulting in 290 civilian fatalities.

Using the Aegis system, Vincennes's captain believed the Iran Air Airbus A300B2 was a much smaller Iran Air Force F-14A Tomcat jet fighter descending on an attack vector, when in fact the Airbus was climbing on its normal civilian flight path [2]. Following this disaster improvements were made to the Aegis system, particularly to the crew interface [3].

The Aegis system correctly identified and reported flight 655's civilian IFF (identification, friend or foe) number, and that it was only flying at 385 knots airspeed; however the crew of Vincennes misinterpreted this information. The U.S. Navy and U.S. Senate investigations were unable to determine which crew member initiated the report that the plane was an F-14, and further recommended Aegis operator training procedures be improved.

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Aegis in other navies

Japan operates four Kongo class destroyers of a modified Arleigh Burke design, with three more planned by 2010 as a result of Japan's fleet review.
Spain is currently operating or building four Alvaro de Bazán class Aegis frigates, with at least two in commission.
Norway is procuring five units of Spanish design and manufacture, as the Fridtjof Nansen class. The first unit of this type, Fridtjof Nansen, was launched on June 3, 2004.
South Korea is building Aegis variants of its KDX destroyers, called KDX-III.
Australia, under its Sea 4000 project to acquire three Air Warfare Destroyers, decided in August 2004 that the Aegis warfare system would be the core of the combat system for the new ships.