Aegis Ballistic Missile Defense Interceptors (SM-3, SM-2 Block IV, and SM-6) (May 2, 2012)

The SM-3 is the U.S Navy’s current exo-atmospheric (above-the-atmosphere) ballistic missile defense interceptor.  It is based on the airframe of the SM-2 Block IV extended-range air defense interceptor, including its two solid-fuel rocket stages.  However the SM-3 replaces this missile’s explosive warhead and radar seeker with an additional solid-fuel  third-stage motor and an infrared-homing, hit-to-kill kill vehicle.

SM-3 Block 0 was an initial version built only for testing.  It was similar to the subsequent Block I version but had specific features added for testing, such as pressure gauges in fuel tanks and rocket motors and an “independent flight termination system.”[1]  The Block 0 was used in the first five intercept tests (FM-2 through FM-6).

SM-3 Block I was a limited production version that provided the first operational Aegis BMD intercept capability aboard the USS Lake Erie in spring 2005.  Only eleven Block Is were built, and four of these were expended in tests (FTM-04-1, FTM-04-2, and Pacific Blitz (2)).

The SM-3 Block IA is the first production version of the SM-3 (the “tactical” missile).  It was first deployed on the USS Shiloh in spring 2006, as part of the initial Aegis BMD 3.6 deployment.

Relative to the Block I, the IA has greater processing capability for improved IR discrimination and eliminated some obsolescence issues and increased missile lifetime. 

The Block IA also has significantly greater divert capabilities.  Starting with the FM-5 intercept test (Block 0, 06/18/2003) an upgraded version of the kill vehicle’s solid divert and attitude control system (SDACS) was employed.  This version of the SDACS has an initial sustain pulse followed by two smaller pulses that provide additional divert capability.  The FM-5 intercept failure was due to a SDACS valve failure involving these two smaller pulses.  Although a repaired version of the valve was used in the pulsed SDACS for the Block I missiles, all of these missiles had the two subsequent pulses disabled.  These pulses were eventually restored in the Block 1A interceptors.

The SM-3 Block IA was first intercept-tested (successfully) in June 2006 and is the version of the SM-3 now deployed on U.S. and Japanese BMD-capable ships.  According to the Congressional Research Service, as of early 2012, a total of 125 SM-3 Block IAs were to be procured, with deliveries to be completed by the end of fiscal year 2014.[2]


Figure 1.  Aegis SM-3 Block IA and Block IB interceptors.  Image source: Laura DeSimone, “Aegis BMD; The Way Ahead,” MDA Briefing Slides, December 6, 2011 (available at: )

The SM-3 Block IB interceptor uses essentially the same missile body as the Block IA, but adds an entirely new kill vehicle with an enhanced infrared seeker, faster processor and improved divert and attitude control system.  After an unsuccessful intercept test in September 2011 (FTM-16 E2), the SM-3 Block IB had is first successful intercept in May 2012 (FTM-16 E2a).  Under current plans, it would begin operational deployment in 2014 on ships equipped with the Aegis BMD 4.0.1 (or 4.0.2) system and in 2015 at the Aegis Ashore site in Romania as part of Phase II of the European Phased Adaptive Approach (EPAA).

The new Block IB kill vehicle will have a new two-color infrared sensor in its seeker (the sensor in the IA version used only a single color).  According to the MDA: “Two-color sensor technology in the SM-3 seeker provides the capability to sense infrared (IR) information in two distinct wavebands, improving the identification of multiple, closely spaced objects.”[3]   The new seeker also has improved sensitivity, giving it a greater detection range against longer range targets.   In addition, the Block IB kill vehicle also has a new, faster Advanced Signal Processor that “increases data processing capability to sort-out and analyze the information gathered by the upgraded seeker.”[4] 

The Block IB kill vehicle also has a new, “more flexible” throttleable divert and attitude control system (TDACS), which improves its divert capabilities.[5]  According to reports, the TDACS is able “to dynamically vary its thrust and operating time” and provides higher thrust levels using continuous thrust management to give a greater divert capability than does the pulsed SDACS in the Block IA.[6]

According to the Congressional Research Service, as of 2012, plans called for the procurement of a total of 472 Block IB missiles through fiscal year 2020 (which is the last year for which data is provided).[7]  In April 2013, the GAO reported that MDA was developing an upgraded “enhanced capability” SM-3 Block IB which could be fielded in the 2015 time frame “to counter advanced threats expected after 2015.”[8]

The SM-3 Block IIA will have entirely new second and third rocket stages giving it a much higher speed than the Block I missiles.  Although no official figures have been released, the Block IA and IB interceptors are typically described as having a burnout speed of about 3.0 km/second, and IIA interceptors about 4.0-4.5 km/second.  This higher speed would allow the Block IIB to cover a much larger geographical area than the Block I missiles and to engage some higher-speed intermediate range missiles.  The Block IIA will also have a new kill vehicle with increased seeker sensitivity, increased divert capability, and a longer operating time once released from its booster rocket.

The Block IIA interceptor is being jointly developed with Japan and is expected to have its first flight in 2015.   It is expected to be deployed operationally in about 2018 with Aegis BMD 5.1 on both ships and at the Polish Aegis Ashore site as part of the EPAA Phase III.


Figure 2.  Evolution of the SM-3 Interceptor.  (Image source: DeSimone)

The SM-3 Block IIB interceptor would have had an even higher speed booster than the Block IIA missile and have been equipped with a new lighter kill vehicle.  Its higher speed was intended to allow it to attempt to intercept potential future Iranian ICBMs from European launch sites.  Block IIB would have been initially deployed sometime after 2020 as part of the EPAA Phase IV.  In March 2013, the Department of Defense announced the cancellation of the Block IIB program.

The modified SM-2 Block IV is the Navy’s current terminal-phase ballistic missile defense interceptor.   The SM-2 Block IV is the Navy’s extended-range air defense interceptor and its airframe is the basis for both the SM-3 and SM-6 interceptors.   It operates within the atmosphere and uses semi-active radar homing and has a high-explosive fragmentation warhead.   A total of 75 SM-2 Block IVs have been modified to give them the ability to attempt to intercept ballistic missiles (three of these have been expended in tests).[9]   The modifications involved changes to the missile’s fuze and autopilot and are less extensive than the changes that would have been made to produce the SM-2 Block IVA missile (which included, among other things, a new infrared seeker) that was cancelled as part of the Navy Area Defense program in December 2001.

The modified SM-2 Block IV was first intercept tested (successfully) against a ballistic missile target in May 2006 (Pacific Phoenix) and has had two other successful ballistic missile intercept tests since.  It began deployment on ships equipped with Aegis BMD 3.6.1 in 2008. The missile is viewed as a stopgap until the BMD version of the SM-6 missile becomes available (currently scheduled for 2015), and it is apparently not compatible with Aegis BMD 4.0.1.


Figure 3.  SM-6 compared to SM-2 Block IV.  (Image source: DeSimone)

The SM-6, currently undergoing development and testing, is the U.S. Navy’s new extended-range air defense interceptor.  It combines the airframe and propulsion system from the current SM-2 Block IV interceptor with the active radar seeker of the current Advanced Medium-Range Air-to-Air Missile (AMRAAM) missile.  Like the SM-2 Block IV, it operates within the atmosphere and uses a high explosive warhead.  The Navy currently plans to buy 1,200 SM-6s.

The initial deployment version of the SM-6 may not have a capability against ballistic missiles.  It is to be given an anti-ballistic missile capability as part of the Sea based Terminal (SBT) Increment 1, which is expected to be deployed in 2015 in conjunction with the Aegis 5.0 CU weapons system.  This is to be followed in 2018 by SBT Increment 2 in which the SM-6 will be deployed in conjunction with Aegis BMD 5.1 weapons system.[10] 

[1]Rear Admiral Brad A. Hicks, “Aegis Ballistic Missile Defense (BMD) System,” The George C. Marshall Institute, December 19, 2005, Figure 6.  Available at:

[2] Ronald O’Rourke, “Navy Aegis Ballistic Missile Defense (BMD) Program: Background and Issues for Congress,” Congressional Research Service, March 19, 2012, p.7

[3] MDA, “FTM-16 Fact Sheet.” Available at:

[4] MDA, “FTM-18 Fact Sheet” June 22, 2012.  Available at:

[5] MDA, “Second-Generation Aegis Ballistic Missile Defense System Completes Successful Intercept Flight Test,” News Release, May 9, 2012.

[6] Zachary M. Peterson, “Raytheon, ATK Hope To Start Advanced SDACS Flight Tests This Year,” Inside Missile Defense, August 30, 2006; “Raytheon and Aerojet demonstrate SM-3 Throttling Divert and Attitude Control System,” PR Newswire US, August 15, 2006.

[7] O’Rourke, p. 7.

[8] Government Accountability Office, “Missile Defense: Opportunity to Refocus on Strengthening Acquisition Management,”   GAO-13-437, April 2013, p. 56.

[9] CRS, March 14, 2013, p. 5.

[10] Raytheon Company, “Standard Missile-6,” available at:; and Shipman Briefing Slides.

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