This post briefly describes the various versions of the Aegis Ballistic Missile Defense (BMD) Weapon System. See the post of May 2 for a description of the different versions of the Aegis BMD interceptor missiles.
Aegis BMD 3.0E: The first deployed Aegis BMD capability was the Aegis Long-Range Surveillance and Tracking (LRS&T) capability using the Aegis BMD 3.0E software. Thus upgrade allowed forward-based Aegis ships to track long-range ballistic missiles and relay this information back for possible use by the U.S. Ground-based Midcourse (GMD) national missile defense system. Several Aegis BMD 3.0E destroyers were forward-deployed in the Pacific as part of the initial GMD Limited Operations Capability in September 2004.
Aegis BMD 3.0: This version provided the first SM-3 engagement capability against ballistic missiles. This “Preliminary Engagement Capability” was intended to provide an emergency capability against short- and medium-range ballistic missiles using the SM-3 Block I interceptor. It also included the LRS&T capability. The first intercept test (successful) using Aegis BMD 3.0 was in February 2005 (FTM-04-1).
Aegis BMD 3.0 was first operationally deployed in spring 2005. This included the deployment of several SM-3 Block I interceptors (of which less than ten were then in existence) aboard the cruiser USS Lake Erie. One other cruiser, the Port Royal, was also upgraded to Aegis BMD 3.0. A significant limitation of Aegis BMD 3.0 was that a ship equipped with it could only perform the BMD mission and not the air defense mission.
Aegis BMD 3.6: Aegis 3.6 was intended to provide engagement capabilities against short-, medium and some intermediate-range ballistic missiles using the new SM-3 Block IA interceptor. Unlike Aegis 3.0 ships, Aegis 3.6 ships were capable of all three missions: ballistic missile engagement, long-range surveillance and tracking, and air defense. Aegis 3.6 was also intended to add a limited launch-on-remote capability using data from another Aegis ship.
Aegis 3.6 was first intercept tested (successfully) in June 2006 (FTM-10) on the Cruiser USS Shiloh, which became the first 3.6 equipped ship in the spring of 2006. It was certified for tactical deployment by the U.S. Navy in September 2006. By the end of 2006, the first destroyer equipped with 3.6 was also operational.
Aegis BMD 3.6.1: Aegis 3.6.1 added a terminal, within-the-atmosphere (endo-atmospheric) ballistic missile defense capability to Aegis 3.6 using the SM-2 Block IV interceptor. Aegis 3.6.1 was first intercept tested (with a SM-2 Block IV) in June 2008 in the successful FTM-14 test.
Aegis 3.6.1 increases the system’s launch-on-remote capabilities by enabling use of data from non-Aegis sensors such as TPY-2 X-band radars and Space Tracking and Surveillance System (STSS) satellites.
All U.S. BMD capable ships have now been upgraded to at least the Aegis BMD 3.6.1 capability. The four current Japanese Aegis BMD destroyers are also equipped with Aegis 3.6.1 or a very similar capability.
Aegis BMD 4.0.1: Aegis 4.0.1 is often described as the “second generation” Aegis BMD system. It is still under development, although the Aegis 4.0.1 computer program has already been installed on several ships. It will add both a new Aegis BMD Signal Processor (BSP) and the new SM-3 Block IB interceptor.
The Aegis BSP signal processor is intended to improve the discrimination capabilities of the Aegis system’s SPY-1 radar. The BSP “enables tracking of individual objects and uses advanced algorithms to identify various objects.” “The Aegis BMD Signal Processor (BSP) provides a real-time identification capability through signal processing. Such processing enables tracking of individual objects and identification though the use of advanced algorithms.”
The Aegis 4.0.1 computer system, and in particular the new signal processor, had been used to observe a number of tests before it was used in an actual intercept attempt. The first intercept test for Aegis 4.0.1 was in September 2011 (FTM-16 E2), although the Block IB interceptor failed to hits is target due a malfunction in its third-stage motor.
The MDA has stated that a 3.6.1 ship can be upgraded to the 4.0.1 system for $45 to $55 million.
Aegis BMD 4.0.2: According to the MDA, this is the Aegis BMD version that was employed in the successful FTM-20 intercept test of February 12, 2013 (which is the only context in which I have seen this designation used). This is likely a new version of the 4.0.1 program to correct for the problem discovered in the FTM-16 E2 intercept test failure, which was due to a problem with the third stage rocket motor thrust pulses. According to the GAO, “a new version of the second generation Aegis weapons system” was developed “to control the amount of time between the pulses,” and that this change “will have minimal consequences on missile performance and ship operations.”
Aegis BMD 5.0. Primarily not about adding new capabilities to the system, this version integrates the Aegis BMD 4.0 system into the Navy’s new Open Architecture modernized version of the Aegis computer system (rather than have the BMD capability on separate adjunct computers as is done in earlier Aegis BMD version) with both anti-aircraft and ballistic missile defense capabilities. The modernized Aegis computer system (Baseline 9) uses commercial-off-the shelf computer infrastructure to enable faster system upgrades and increased commonality, and to facilitate the addition of BMD capabilities to additional ships. However, Aegis 5.0 will apparently not have the within-the-atmosphere terminal-phase BMD capability that Aegis 4.0 has. Several ships have already been upgraded to the Aegis 5.0 BMD computer system.
Aegis BMD 5.0 CU (capability upgrade) is intended for deployment by 2015. This restores a terminal within-the-atmosphere BMD capability with the Sea-Based Terminal Increment 1 using SM-2 Block IV and modified SM-6 interceptors. It also expands and updates the Aegis Baseline 9 MRBM and IRBM threat set to include EPAA Phase II threats and increases the maximum number of SM-3 missiles that can be simultaneously in flight to be able to deal with larger attacks. The Aegis Ashore system scheduled for Romania in 2015 will initially be deployed with Aegis BMD 5.0 CU (although apparently without the terminal interceptors).
Aegis BMD 5.1 is scheduled to begin deployment in 2018. It will integrate the new high-speed SM-3 Block IIA interceptor onto U.S. and Japanese ships. It will have improved data links to permit engage-on-remote operation and will be able to engage longer-range missiles, including all IRBMs. It will improve terminal phase capabilities with addition of the Sea-Based Terminal Increment 2 (I don’t know how this differs from Increment 1) using modified SM-6 interceptors. The Aegis Ashore site scheduled for Poland in 2018 will initially be deployed with Aegis 5.1.
 Martin Stieff, “BMD Watch: U.S. Navy Certified Aegis 3.6,” UPI September 19, 2006.
 According to the Congressional Research Service, the Japanese ships have “at least an approximate equivalent of the 3.6.1 version of the Aegis BMD System.” Ronald O’Rourke, “Navy Aegis Ballistic Missile Defense (BMD) Program: Background and Issues for Congress, RL33745, March 14, 2013, p. 11.
 MDA, “FTM-18 Fact Sheet” June 22, 2012. Available at: http://www.mda.mil/global/documents/pdf/Aegis_FTM-18_FactSheet.pdf
 MDA, “Aegis Ballistic Missile Defense FTM-16 Factsheet,” August 22, 2011, Available at: http://www.stratcom.mil/files/FTM-16%20Fact%20sheet%20-%20v13.pdf.
 MDA, “FTM-16 Fact Sheet.”
 O’Rourke, p. 3.
 Vice Admiral J. D. Syring, “Ballistic Missile Defense Update,” presentation to the American Society of Naval Engineers, February 22, Slide 15.
 GAO-13-432, p. 53.
 PB 2014 Missile Defense Agency, PE 0603892C: Aegis BMD, April 2013, p. 2a-343.