Aegis Combat System: How the Navy’s Missile Shield Works
Aegis combat system explained: the SPY radar, SM-3 and SM-6 interceptors, the ships that carry it, and Aegis Ashore in Romania and Poland.
Short answer: The Aegis combat system is the U.S. Navy’s integrated radar, computer and missile system that protects warships, and in many cases whole regions, from air and missile attack. Its core is the SPY phased-array radar, which can search, track and guide missiles at the same time. Aegis is fitted to the Navy’s Ticonderoga-class cruisers and Arleigh Burke-class destroyers, and its ballistic missile defense version uses SM-3 and SM-6 interceptors. There are also two land-based Aegis Ashore sites, in Romania and Poland.
Last updated: October 28, 2026
- What it is: an automated command-and-control and weapons control system, “from detection to kill”
- Radar: AN/SPY phased array, with a track capacity of more than 100 targets
- Ships: Ticonderoga-class cruisers and Arleigh Burke-class destroyers
- First Aegis ship: USS Ticonderoga, commissioned in 1983
- Missile defense interceptors: SM-3 (midcourse) and SM-6 (terminal)
- BMD-capable ships: 63 expected by the end of fiscal 2026 (MDA, via CRS)
What the Aegis combat system does
The Navy’s Aegis fact file describes Aegis as “a centralized, automated, command-and-control (C2) and weapons control system that was designed as a total weapon system, from detection to kill.” The name comes from the mythological shield of Zeus.
Aegis links a ship’s sensors, computers, displays and weapon launchers so that one system can handle threats in the air, on the surface and under the sea. The Congressional Research Service notes that it was originally developed in the 1970s to defend ships against aircraft, anti-ship cruise missiles, surface threats and submarines.
The SPY radar at its heart
The Navy calls the AN/SPY radar “the heart of the system.” It is a multi-function phased-array radar, which steers its beam electronically rather than by rotating an antenna. The Navy says it can perform “search, track and missile guidance functions simultaneously, with a track capacity of more than 100 targets.”
The first engineering model of the SPY-1 was installed on the test ship USS Norton Sound in 1973. The newest Arleigh Burke destroyers, known as Flight III, carry the SPY-6 radar, which CRS describes as more capable than the SPY-1 on cruisers and earlier destroyers.
Which ships carry Aegis
CRS says all but three of the Navy’s cruisers and destroyers are Aegis ships. The exceptions are the three Zumwalt-class destroyers, which use a different combat system.
Ticonderoga-class cruisers. The first Aegis ship, USS Ticonderoga, was commissioned in 1983. The Navy procured 27 cruisers, and CRS says seven remained in service as of October 1, 2025, with the last two projected to retire in fiscal 2027.
Arleigh Burke-class destroyers. The lead ship, USS Arleigh Burke, was commissioned on July 4, 1991. CRS says 97 had been procured through fiscal 2025, with 76 in service as of October 1, 2025.
Aegis has also been sold to allies. CRS lists Japan, South Korea, Australia, Spain and Norway as countries that operate, are building or plan to build Aegis-equipped ships. Our guide to types of warships explains where destroyers and cruisers fit in a fleet.
Aegis ballistic missile defense
The Aegis ballistic missile defense (BMD) program, run by the Missile Defense Agency (MDA) and the Navy, upgrades Aegis ships to track and shoot down ballistic missiles. CRS quotes MDA’s fiscal 2026 budget as saying “by the end of FY 2026, there will be 63 total BMD capable [Aegis] ships.”
According to the Missile Defense Agency, Aegis BMD defeats short- to intermediate-range ballistic missiles in the midcourse phase with the SM-3, and short-range ballistic missiles in the terminal phase with the SM-6. MDA says that in 2020 an Aegis destroyer intercepted a simple ICBM-representative target with an SM-3 Block IIA.
| Feature | SM-3 | SM-6 |
|---|---|---|
| Phase of flight | Midcourse, above the atmosphere | Terminal, inside the atmosphere |
| Kill method | Hit-to-kill kinetic vehicle | Not specified in the cited sources |
| Current versions | Block IA, Block IB, Block IIA | SM-6 (BMD-capable versions) |
| Targets | Short- to intermediate-range ballistic missiles | Short-range ballistic missiles; also used for air defense |
| Notable detail | Block IIA co-developed with Japan, 21 inches in diameter along its full length | Replaced the SM-2 Block IV as the sea-based terminal interceptor |
Our reports on the SM-3 Block IB contract and SM-6 contract cover recent production orders.
Aegis Ashore in Romania and Poland
Aegis Ashore is the land-based version. CRS says there are two sites, one in Romania and one in Poland, each with an Aegis deckhouse-style structure and 24 SM-3 missiles in a relocatable vertical launch system. They were announced in 2009 as part of the European Phased Adaptive Approach to defend Europe against ballistic missiles from countries such as Iran.
MDA says the Romania site was certified operational in 2016. CRS cites MDA testimony that the Poland site, at Redzikowo, was delivered to the Navy on October 1, 2023.
CRS also notes that four BMD-capable destroyers are based at Rota, Spain, and that the Navy says they provide Mediterranean presence equivalent to about 10 ships based on the U.S. East Coast.
Defending against hypersonic threats
Aegis is being upgraded for newer threats. CRS quotes an MDA release saying that in March 2025 the destroyer USS Pinckney detected, tracked and performed a simulated engagement of a maneuvering hypersonic target using the latest Aegis software. For more on that threat, see our explainer on hypersonic missiles and our guide to THAAD missile defense.
Peter’s World’s view
Aegis has lasted more than four decades because it was designed as a whole system that could be upgraded piece by piece: new radars, new software baselines and new missiles. The official figures show a fleet transition under way, with the last Aegis cruisers leaving service and Flight III destroyers bringing a new radar. The demand side keeps growing too, as the same ships are asked to defend against aircraft, ballistic missiles and now hypersonic weapons.
Frequently asked questions
What is the Aegis combat system?
It is the U.S. Navy’s integrated system of radar, computers and missiles that detects, tracks and destroys air, surface and missile threats.
Which ships have Aegis?
U.S. Navy Ticonderoga-class cruisers and Arleigh Burke-class destroyers, plus ships in allied navies such as Japan, South Korea, Australia, Spain and Norway.
Can Aegis shoot down ballistic missiles?
Yes. BMD-capable Aegis ships use the SM-3 in the midcourse phase and the SM-6 in the terminal phase.
How many targets can the Aegis radar track?
The Navy says the SPY radar has a track capacity of more than 100 targets.
What is Aegis Ashore?
Aegis Ashore is the land-based version of Aegis BMD. There are two sites, in Romania and Poland, each with 24 SM-3 missiles.
When did Aegis enter service?
The first Aegis ship, USS Ticonderoga, was commissioned in 1983.
This article was written by Peter with AI assistance and checked against the sources linked. See our AI use disclosure.
Sources
- U.S. Navy: Aegis weapon system fact file
- Congressional Research Service: Navy Aegis Ballistic Missile Defense Program (RL33745)
- Missile Defense Agency: Aegis Ballistic Missile Defense
