The Aegis combat system has been the undisputed champion of naval air defense since the USS Ticonderoga entered the U.S. fleet in 1983. The United States currently has 22 cruisers and 49 destroyers in service with this system, with another 13 destroyers on the way. Recently, though, a new system is on the way, the Principal Anti-Air Missile System (PAAMS).
PAAMS is slated to enter service with three navies - the Daring-class destroyers in The United Kingdom, the Forbin-class destroyers in France, and the Andrea Doria-class destroyers in Italy. This system operates the ASTER family of surface-to-air missiles. There are two versions of the ASTER, the ASTER-15 and the ASTER-30. The ASTER 15 is a point-defense system, with a range of 30 kilometers. It has been installed on the Formidable-class frigates in the Singaporean Navy and the al-Riyadh class frigates in the Saudi Navy. The other missile in the family is the ASTER 30, with a range of to 70 kilometers. This will be on the destroyers. The ASTER missiles are guided by a variant of the active-radar seeker used on the Mica air-to-air missile
The missile used with the Aegis system is the Standard missile. This missile comes in two varieties. The first is the SM-1, which has a range of 37 kilometers. This was primarily used on older vessels and it is largely being replaced by the Evolved Sea Sparrow Missile (ESSM), which has a range of 33 kilometers. The ESSM's advantage over the SM-1 is that four ESSMs can fit into one VLS cell - as opposed to one SM-1. The other missile is the SM-2, which has a range of up to 111 kilometers. The SM-2 is on every one of the Ticonderoga-class cruisers and Arleigh Burke-class destroyers. The Standard and ESSM missiles are semi-active - they home in on reflected radar emissions. Aegis has been exported to Japan (for use on the Kongo and Atago-class destroyers) Spain (for use on the Bazan-class frigates), and Norway (for the Nansen-class frigates).
Which system is better? While PAAMS is newer, the Aegis system has had a track record of over 20 years of superb performance (the 1988 shoot down of an Iranian airliner was the result of human error). The missiles also have a slightly longer range. The gap is close, though. That said, the gap exists, with a slight edge to the more numerous Aegis vessels (84 vessels compared to 12 for PAAMS). - Harold C. Hutchison (email@example.com)