The Aegis ship based missile defense system is the sea-based component of the Ballistic Missile Defense System (BMDS). It can intercept short to medium-range ballistic missiles as well as cruise missiles using variations of the Standard Missile-2 (SM-2), Standard Missile-3 (SM-3), and Standard Missile-6 (SM-6). The system is integrated on certain U.S. Navy Ticonderoga-class cruisers and Arleigh Burke-class destroyers, allowing the Missile Defense Agency (MDA) to move its defense capabilities closer to adversaries’ launch sites. This element is one layer of the overall BMDS and the primary interceptor for the European Phased Adaptive Approach (EPAA).

System Elements

The Aegis combat system was originally designed for defending ships against aircraft and anti-ship cruise missiles during its development in the 1970s and initial deployment in 1983. The system has undergone a number of upgrades since then, including adding a ballistic missile defense mission. In 2004, the Aegis system began its support for ballistic missile defense missions by serving as a surveillance and tracking radar for intercontinental ballistic missiles (ICBM). The system then upgraded to an initial engagement capability in 2005 and terminal capability in 2006. In 2008, the Aegis system was used to intercept a non-functioning satellite as part of Operation Burnt Frost.1

Envisioned roles for the Aegis BMD ships have varied over the years. Some have proposed using the Aegis ships for homeland and coastal defense missions while Aegis ships are on mandatory rotations at home ports in the United States. There have also been proposals to station Aegis BMD ships close to adversary coasts and produce variants of the interceptors that would reach speeds sufficient to intercept ballistic missiles in the boost phase.2 The cancelled Phase 4 of the European Phased Adaptive Approach envisioned the SM-3 Block IIB interceptor, which would have had a limited capability to intercept an Iranian ICBM targeted at the United States mainland even from forward deployments in Europe.3

The first mission that Aegis BMD ships filled was as Long Range Tracking and Surveillance radars in support of the Ground-based Midcourse Defense system in 2004. This mission involved deploying Aegis ships at forward bases to pick up missile tracks for ICBMs directed at the United States. At present, each Aegis ship utilizes the AN/SPY-1 radar to track up to 100 targets simultaneously. Upgraded versions of the Aegis software like the Baseline 9.C1 software configuration allow the ships to simultaneously track ballistic missiles and air and cruise missile threats. Newer ships are also equipped with either the AN/SPY-1B, AN/SPY-1B (V), or AN/SPY-1D upgraded radars. The Flight III Arleigh Burke-class destroyers are also scheduled to feature the Air and Missile Defense Radar.

Aegis systems have test “launch on remote” capability where an interceptor can use off-board radars to pick up the initial track of a threatening missile and then on-board radars for final tracking and intercept. The first test of this concept coincided with the completion of Phase 1 of the EPAA in 2011, a test that included an SM-3 Block IA interceptor receiving information from am AN/TPY-2 radar.4 In 2013, another launch on remote test proved the capability to integrate Space Tracking and Surveillance System Demonstrators (STSS-D) data for an intercept with an SM-3 Block IA illustrating the expanded battlespace such a capability provides.5 Phase 3 of the EPAA is also scheduled to include an engage on remote capability for Aegis interceptors to conduct operations based entirely on off-board radar information, expanding the range of the Aegis systems even further.6

The Navy currently deploys 33 Aegis BMD-capable ships in its fleet. It is currently undertaking an effort to modernize ships with older 3.6 and 4.0 versions of the BMD capability to the 5.0 Capability Upgrade.7 Initial plans to upgrade all of the BMD ships to the version 5.0 foundered under the pressure of budget cuts imposed by sequestration, forcing the Navy to commit to only upgrading all current 3.6 version ships to the 4.0 version and then only upgrading seven ships to the 5.0 version configuration.8 These cuts affect the ability of the ships to process radar information from multiple sources and track aircraft, cruise missile, and ballistic missile threats simultaneously.

Budget issues have also affected the Navy’s projections of the number of Aegis BMD capable ships that it will be able to deploy in the future.  The Navy has proposed to eliminate the BMD capability on five of its Aegis cruisers during scheduled modernization in favor of upgrading Aegis Destroyers with BMD capabilities.9 In addition, prior MDA estimates of the number of BMD capable ships it would procure did not account for the training time required for new hulls, meaning earlier estimates had to be revised downward from an earlier 48 to 39 in FY2020.10 These estimates were revised after the decision was also announced in the FY 2016 budget that the Navy would cut the BMD upgrades from the modernization plan of five of its ships.11

In addition to the United States deployment of Aegis ships, Japan also currently deploys four Aegis BMD KONGO-class destroyers with plans to upgrade its other two Aegis capable destroyers and build two more BMD-capable Atago-class cruisers with BMD capability version 5.0 for a final total of eight.12 Japanese ships have conducted four flight tests of Aegis interceptors, including three successful intercept tests. Japan also cooperates with the United States on the development of the SM-3 Block IIA interceptor.


  1. “Aegis Ballistic Missile Defence (BMD) System, United States of America,” Naval Technology,
  2. James M. Lindsay and Michael E. O’Hanlon, Defending America: The Case for Limited National Missile Defense (Washington D.C.: Brookings Institution, 2001)
  3. “US scraps final phase of European missile shield,” BBC, March 16, 2013,
  4. Scott Truver, “Aegis Silences the Critics,” Defense News, May 2, 2011,
  5. MDA News Release, “Aegis Ballistic Missile Defense Intercepts Target Using Space Tracking and Surveillance System-Demonstrators (STSS-D) Data,” Missile Defense Agency, February 13, 2013,
  6. Ronald O’Rourke, “Navy Aegis Ballistic Missile Defense (BMD) Program: Background and Issues for Congress,” (Washington D.C.: Congressional Research Service), December 11, 2015,
  7. Ibid.
  8. Sam LaGrone, “Navy Altered Destroyer Upgrades Due to Budget Pressure, Demand for Ships,” USNI News, June 3, 2014,
  9. O’Rourke, December 11, 2015.
  10. Sam LaGrone, “MDA Quietly Revises Projected Ballistic Missile Defense Ship Totals Down from FY 2016 Budget Request,” USNI News, September 1, 2015,
  11. Sam LaGrone, “Navy Again Reduces Scope of Destroyer Modernization, 5 Ships Won’t Receive Any Ballistic Missile Defense Upgrades,” USNI News, March 3 2015,
  12. O’Rourke, December 11, 2015.