The Sea-Based Terminal Program and the SM-6 Dual Interceptors (July 25, 2016)

Sea-Based Terminal

Most of the attention given the US Navy’s Aegis Ballistic Missile Defense (BMD) program focuses on its various versions of the SM-3 anti-missile interceptor.  These missiles, the SM-3 Block IA, the SM-3 Block IB and the forthcoming SM-3 Block IIA, intercept their targets above the atmosphere and are intended to provide coverage over large areas (particularly the Block IIA).  However, this post discusses the Missile Defense Agency’s and the Navy’s Sea-Based Terminal (SBT) program, which is developing and deploying lower-altitude, within-the atmosphere ballistic missile defense interceptors.

An SBT capability offers several possible benefits.  First, it provides a second layer of ballistic missile defense for Navy ships and nearby areas, thereby potentially increasing the overall effectiveness of the Aegis BMD system.  SBT interceptors operate in a completely different way than the SM-3 interceptors.  The SBT interceptors home in on their target using radar, maneuver using atmospheric forces, and kill with a high-explosive fragmentation warheads, while SM-3 interceptors use infrared homing, maneuver using rocket thruster (divert thrusters), and kill using direct high-speed collisions.  These differences in operating principles may make it less likely that a countermeasure (or other circumstance) that defeats an SM-3 interceptor can also defeat an SBT interceptor.  Second, SBT interceptors can potentially intercept shorter-range missiles, such as Scuds (or longer range missiles on depressed trajectories) that do not leave the atmosphere (that is, rise above about 100 km altitude) and thus cannot be intercepted by SM-3 interceptors.  Third, SBT interceptors are likely to be much less expensive, by a factor of three or more, than SM-3 interceptors.  Finally, SBT interceptors can also be used to intercept aircraft (and soon ships), allowing more efficient use of the limited number of vertical launch tubes on Navy ships.

SM-2 Block IV, Block IVA, and Block IV (modified)

In the 1990s, the Ballistic Missile Defense Organization and the U.S. Navy planned to develop a terminal phase ballistic missile defense system known as Navy Lower Tier.  (In parallel, BMDO was developing the Navy Upper Tier interceptor, which was renamed Navy Theater Wide, and eventually evolved into the current SM-3 Aegis BMD interceptors.)  This program, which was renamed Navy Area Defense in 1996, was based on a new version of the Navy’s existing extended-range air defense missile the SM-2 Block IV.  The SM-2 Block IV operates within the atmosphere, uses semi-active radar homing and has a high-explosive fragmentation warhead.

The new missile, to be known as the SM-2 Block IVA, would have had a new side-mounted infrared terminal seeker as well as modifications to the Block IV’s guidance system, fuzing system and warhead (see figure 1 below).  However, in December 2001, the Department of Defense cancelled the Navy Area Defense system, citing “poor performance and projected future cost and schedules” following a Nunn-McCurdy cost breach.[1]


Figure 1.  Modifications to the SM-2 Block IV to produce the SM-2 Block IVA.  Missile Defense Agency image (

Despite the cancellation of the Navy Area Defense Program, the Navy retained interest in developing a Sea-Based Terminal capability and considered, for example, the possibility of developing a sea-based version of the Patriot PAC-3 system.[2]  Ultimately, following a successful intercept test of a modified SM-2 Block IV interceptor against a short-range ballistic missile in 2006 (see list of SBT tests below), the MDA and the Navy decided to develop an interim sea-based terminal missile defense system by modifying existing SM-2 Block IV interceptors.  The modifications to the Block IV interceptors involved changes to the missile’s fuze and autopilot and were less extensive than the changes that would have been made to produce the cancelled SM-2 Block IVA missile.  At the time, the Navy had about 100 Block IV interceptors in inventory, and ultimately 75 were modified for ballistic missile defense (5 of which have subsequently been expended in tests). The modified SM-2 Block IV was first intercept tested (successfully) against a short-range ballistic missile target in May 2006 (Pacific Phoenix) and has had three other successful ballistic missile intercept tests since (one test involved two interceptors).

Deployment of the modified Block IV missiles began in 2008 on ships equipped with the basic Aegis BMD 3.6.1 system.  At the end of 2008, there were about 18 ships with this version of the Aegis system.  This number that would grow to about 24 in 2012 and then decline as 3.6 ships were upgraded to higher version of the Aegis BMD system.

The Block IV interceptor was only intended to provide an interim “gap-filler capability” until a new (then undefined) SBT interceptor could be deployed.[3]  Accordingly, and as a cost-saving move, ships that were upgraded to Aegis BMD 4.x and early versions of 5.x (Phase II of the European Phased Adaptive Approach (EPAA)) would not be equipped for the Modified Block IV interceptors and thus would not have any SBT ballistic missile defense capability.  A sea-based terminal capability would then be restored with Aegis 5.2 as part of phase III of the EPAA using the new SBT interceptor.  However, a recent MDA slide now indicates that ships with either Aegis BMD 4.1 or 5.0 CU will be able to operate SBT interceptors.[4]

The SM-6 Interceptor

Ultimately, the Navy decided that the longer-term SBT interceptor would be based on its new SM-6 new extended-range air defense interceptor.  The SM-6 combines the airframe and propulsion system from the SM-2 Block IV interceptor with the active radar seeker of the advanced Medium-Range Air-to-Air Missile (AMRAAM) missile.  See figure 1 below.  Like the SM-2 Block IV, it operates within the atmosphere and uses a high explosive warhead.  As of 2013, the U.S. Navy planned to procure total of 1,800 SM-6 missiles by FY 2024[5]  The SM-6 was first deployed in December 2013 (on DDG-100) and the Navy has so far accepted deliveries of over 250 missiles.[6]


Figure 2.  SM-6 compared to SM-2 Block IV.  Image source: Laura DeSimone, “Aegis BMD; The Way Ahead,” MDA Briefing Slides, December 6, 2011 (available at: )

The SM-6 has an over-the-horizon capability against aircraft using targeting data provided by other ships or by aircraft, such as the Navy’s E2-D Hawkeye airborne warning and control system (AWACS) airplane.  An upgraded version, the SM-6 Block IA, adds “guidance section hardware and software modifications,” including the incorporation of GPS guidance, to enable attacks on sea or land targets.[7]  In a January 2016 test, an SM-6 struck and sank a decommissioned U.S. Navy frigate.[8]  Current plans call for SM-6 missiles with an anti-ship capability to begin deployment in fall 2016.[9]


The SM-6 Dual I and Dual II Interceptors

The initial version of the SM-6 did not have a capability against ballistic missiles. The SM-6 is to be given a terminal-phase anti-ballistic missile capability in two phases.  The first phase, the SBT Increment 1, includes an upgraded missile known as the SM-6 Dual I.  A Dual I interceptor successfully intercepted a short-range (less than 1,000 km) ballistic missile target in a July 2015 test and its deployment is expected to begin in 2016.[10] This is to be followed in 2018-2019 by SBT Increment 2 which will include the Dual II version of the SM-6.  The SM-6 Dual interceptors will eventually supplant the modified Block IV interceptors as the Navy’s SBT interceptors.

There appears to be little publicly available information about how the Dual I interceptor differs from the baseline SM-6 or SM-6 Block I, or how the Dual II missile differs from the Dual I.  Press reports indicate that the Dual I has a more powerful processor and additional software.[11]  A Raytheon spokeswoman described the Dual I as containing both ballistic missile defense and anti-air warfare software in the same missile.[12]

SBT Testing

The modified SM-2 Block IV has had four successful intercept tests against ballistic missile targets and the SM-6 Dual I had its first successful test in July 2015.  All of these tests were against short-range ballistic missile targets.  The next SM-6 Dual I test will be against a medium-range (1,000-2,000 km) ballistic missile.  The tests are summarized below:

Pacific Phoenix (May 24, 2006): A modified SM-2 Block IV launched from the cruiser Lake Erie successfully intercepted short-range ballistic missile in the terminal phase of its flight in a joint U.S. Navy and MDA test.[13]  This was the first sea-based intercept of a ballistic missile.  The cruiser was equipped with an interim Aegis missile defense capability known as “Linebacker.”[14]


Flight Test Standard Missile-14 (FTM-14) (June 5, 2008):  A short-range ballistic missile target was successfully intercepted in its terminal phase by two modified SM-2 Block IVs salvo fired by the cruiser Lake Erie which was equipped with  Aegis BMD 3.6.1.[15]  The intercept occurred at an altitude of about 12 miles.


Stellar Daggers (March 26, 2009): A short-range ballistic missile target was successfully intercepted by a modified SM-2 Block IV interceptor launched from the destroyer Benfold.[16]   The destroyer simultaneously intercepted a cruise missile target with an SM-2 Block IIIA interceptor.  The test was conducted by the U.S. Navy rather than by MDA.


Multi-Mission Warfare Event 1 (MMW E1) (July 29, 2015):  A SM-6 Dual I missile, launched from the destroyer John Paul Jones (Aegis BMD 5.0 CU, Aegis Baseline 9.C1), successfully intercepted short-range ballistic missile (SRBM).[17] This was the first flight and intercept test for the SM-6 Dual I.

In two separate tests on July 31 and August 1, SM-6 Dual I interceptors successfully intercepted cruise missile targets (although in the second test, the interceptor warhead was intentionally not detonated in order to be able to reuse the target).

Multi-Mission Warfare Event 2 (MMW E2) (July 30, 2015): A SM-2 Block IV missile, launched from the destroyer John Paul Jones (Aegis BMD 5.0 CU, Aegis Baseline 9.C1), successfully intercepted a SRBM.[18]

Flight Test Other-21 (FTX-21) (May 17, 2016): An Aegis destroyer (John Paul Jones) successfully tracked a medium-range ballistic missile (MRBM), including its reentry and subsequent flight within the atmosphere.[19]  This is the first time Aegis had tracked an MRBM within the atmosphere during reentry.  The plan for this test had originally included an intercept by an SM-6 Dual I, but for range safety reasons the intercept attempt was deferred until the FTM-27 test in late 2016.[20] Department of Defense budget documents describe the test as “SM-6 Dual I missile simulated engagement of a Medium Range Ballistic Missile.”[21]

FTM-27 (1Q, FY 2017):  Two SM-6 Dual I interceptors will be salvo fired against a MRBM target.

FTX-24 (4Q FY 2017):  Simulated Sea-Based Terminal (SM-6 Dual) intercept of separating short-range ballistic missile.[22]  Actual target, but no interceptor will be fired.

FTM-28 (3Q, 2018): SBT intercept test.[23]

FTM-31 (1Q FY 2019): SBT intercept test[24]

FTM-33 (1Q FY 2019): SBT intercept test[25]

FTM-32 (3Q FY 2019): SBT intercept test[26]


[1] Department of Defense, “Navy Area Missile Defense Program Cancelled,” News Release, December 14, 2001.  Online at

[2] Malina Brown, “Navy Rebuilding Case for Terminal Missile Defense Capability,” Inside the Navy, April 19, 2004.

[3] John Liang, “Obering: ’Limited’ Sea-Based Aegis Terminal Competition RFP Out Soon,” Inside Missile Defense,

August 27, 2008.

[4] Figure 1 of Ronald O’Rourke, “Navy Aegis Ballistic Missile Defense (BMD) Program: Background and Issues for Congress,” Congressional Research Service, CRS Report RL33745, May 26, 2016.  Figure shows a slide provided to the CRS by the Missile Defense Agency on March 25, 2016.

[5] Jason Sherman, “New Threat Analysis Prompts $3B increase in SM-6 Procurement Spending,” Inside the Navy, September 9, 2013.

[6] Lee Hudson, “Raytheon Exec: Standard Missile-6 Price Slashed by 32 Percent,” Inside the Navy, July 14, 2014; Raytheon Company, “SM-6 Shatters Engagement Distance Record,” News Release, March 7, 2016.

[7] Jason Sherman, “Navy, Raytheon Ready New Satellite-Guided, Standard Missile-6 Variant,” Inside the Pentagon, July 3, 2014.

[8] Sam LaGrone, “Navy Sinks Former Frigate USS Reuben James in Test of New Supersonic Anti-Surface Missile,” USNI News, March 7, 2016.

[9] Justin Doubleday, “Navy To Deploy Modified SM-6 with Anti-Ship Capability this Fall,” Inside Defense SITREP, March 10, 2016.

[10] According to MDA Director Vice Admiral James Syring’s 2016 Congressional Prepared Statement, the SM-6 Dual I “will enter the fleet inventory this spring.” Online at

[11] Sydney J. Freeberg Jr., “SM-6 Can Now Kill Both Cruise AND Ballistic Missiles,”, August 4, 2015; Kyong M. Song, “Naval Interceptor Takes on both Ballistic and Cruise Missiles, Aerospace America, September 2015, p. 6.

[12] Jason Sherman, “Aegis-Guided SM-6 Interceptor Shoots Down Ballistic Target,” Inside Missile Defense, August 4, 2015.

[13] Missile Defense Agency, “First at-Sea Demonstration of Sea-based Terminal Capability Successfully Completed,” News Release, May 24, 2006.

[14] Staff writers, “Aegis Destroys Ballistic Missile in Terminal Phase,” Space Daily, June 4, 2008.

[15] Missile Defense Agency, “Successful Sea-Based Missile Defense Intercept,” News Release, June 5, 2008; Staff writers, “Aegis Destroys.”

[16] U.S. Third Fleet. “Navy Completes Air and Ballistic Missile Exercise,” News Release. March 27, 2009; “Raytheon Standard Missile-2 Demonstrates Sea-Based Terminal, Fleet Protection,” PR Newswire, March 27, 2009.

[17] Missile Defense Agency, “Aegis Ballistic Missile Defense System Completes Successful Series of Intercept Flight Test Events,” News Release, August 3, 2015.

[18] MDA, “Aegis Ballistic Missile Defense System Completes.”

[19] Missile Defense Agency, “Aegis BMD System Completes Successful Tracking of Medium-Range Ballistic Missile Target,” News Release, May 17, 2016.

[20] Jason Sherman. “Aegis BMD Tracks Ballistic Missile Target Within Earth’s Atmosphere,” Inside the Pentagon, May 19, 2016.

[21] Department of Defense, President’s Budget (PB), FY 2017, MDA, RDT&E, p. 2a-656.

[22] PB FY 2017, pp. 2a-657, 2a-678, 2a-708.

[23] PB FY 2017, p. 2a-679.

[24] PB FY 2017, p. 2a-679.

[25] PB FY 2017, p. 2a-679.

[26] PB FY 2017, p. 2a-679.

THAAD Radar Ranges (July 17, 2018)

A central element of the debate surrounding the recent decision by South Korea to allow the United States to deploy a Terminal High Altitude Area Defense (THAAD) missile defense system on its territory is the range of the THAAD’s radar. China argues that the THAAD radar will be able to look deep into its territory; supporters of the deployment counter that the radar will be configured so that its range will be limited.

The radar used with a THAAD battery is the X-band AN/TPY-2.  The TPY-2 radar has two configurations.  It can be configured as Terminal Mode (TM) radar, in which it operates as the fire control radar for a THAAD battery.  Alternatively, it can be set up as a Forward-Based Mode (FBM) radar, in which it relays tracking and discrimination data to a remote missile defense system, such as the U.S. Ground-Based Midcourse (GMD) system.  If THAAD is deployed to South Korea, The United States has stated that its TPY-2 radar would be in the shorter-range TM configuration.  Since in the TM mode, the radar reportedly only has a range of 600 km, supporters of the THAAD deployment argue that while its range is adequate to cover N. Korea, it cannot look deeply into China.  Critics of this argument point out that in the FBM mode the radar has a much greater range, and that the radar can be converted from TM to FBM (or vice versa) in only eight hours or less.  According to a U.S. Army manual, “The hardware used by the two modes is identical, but their controlling software, operating logic, and communications package are different.”[1]  In addition the radar is highly mobile: it can be transported by air and can be operational with four hours of reaching its deployment site.

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THAAD Flight and Intercept Tests Since 2005 (July 10, 2016)

Flight tests of the Terminal High-Altitude Area Defense (THAAD) system since developmental testing resumed in 2005 and planned future tests.


Figure 1. THAAD intercept tests since 2005. In April 2012, the Director of Operational Test and Evaluation stated that “due to budget constraints within the agency, MDA had decided to slow the pace of THAAD testing to about one test every eighteen months.[1] 

FTT-01 (November 22, 2005:  First launch of an operationally-configured THAAD interceptor.[2]  The launch, conducted at the White Sands Test Range (WSMR), successfully demonstrated the operation of missile and kill vehicle, although no target was used and thus no intercept was attempted.  The THAAD TPY-2 radar does not appear to have participated in this test.

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SM-3 Block IIA Testing Chronology (July 7, 2016)

SM-3 Block IIA Testing Chronology

SCD PTV-01 (October 2013): SM-3 Cooperative Development (SCD) Propulsion Test Vehicle (PTV)-01. A test of the Block IIA booster rocket and canister, reportedly successful, intended to demonstrate that The Block IIA could be launched from the Vertical Launching System used on U.S. Navy Aegis ships and at Aegis Ashore sites.

SCD CTV-01 (June 6, 2015): SCD Controlled Test Vehicle (CTV)-01.  First flight test of SM-3 Block IIA.  It was not an intercept test and no target was present.  The Missile Defense Agency stated that the test “successfully demonstrated flyout through nosecone deployment and third stage deployment.”[1]  According to the Government Accountability Office (GAO), the test was delayed by about 5 months.[2]

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Strategic Capabilities of SM-3 Block IIA Interceptors (June 30, 2016)

In two previous posts, I made estimated projections forward in time of the number of U.S. Navy ballistic missile defense (BMD) capable ships and the number of SM-3 BMD interceptors.[1]  These projections reached two main conclusions: (1) The number of BMD capable ships would reach the upper seventies (77) by 2040; and (2) The number of SM-3 Block IIA interceptors (including possible more advanced version of the missile) would be in the hundreds, possibly 500-600 or more, by the mid-to-late 2030s.

Several developments since those posts were written illustrate the uncertain nature of such projections.  In February 2016, it was revealed that the Navy had decided to upgrade three additional Flight IIA Aegis destroyers to the full advanced BMD capability (under the previous plan these three ships would have had no SM-3 BMD capability).[2]  In addition, it is still unclear how long the five Aegis BMD cruisers will remain in service, although this makes no difference to the longer term projections..

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Update on Future Ground-Based Midcourse (GMD) Flight Tests (April 20, 2016)

An updated description of planned GMD flight tests (last update was my post of April 12, 2015) as best I can reconstruct them.  Between now and mid-2021, it appears that MDA plans five intercept and one non-intercept test of the GMD system.

FY 2017:

FTG-15 (1Q FY 2017).  This is scheduled to be the first intercept test since FTG-06b in July 2014.  It will be the first GMD intercept test against an ICBM-range target (range greater than 5,500 km).  The target will include countermeasures.  FTG-15 will  also will be the first flight and intercept test of the new production CE-II Block-I version of the Exo-Atmospheric Kill Vehicle (EKV) and the first flight test of the upgraded C2 booster.   According to Admiral Syring, in this test “…we’re getting now out to the long-range and closing velocities that certainly would be applicable from a North Korean or Iran type of scenario.” [1]


FTG-15 (Image source: MDA)

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Updated List of Claims about GMD Effectiveness (April 14, 2016)

This is an updated list (previous version was June 16, 2015) of claims by U.S. government officials about the effectiveness of the U.S. Ground-Based Midcourse (GMD) national missile defense system.  It adds four additional claims (#33, #34, #35 and #36).

(1) September 1, 2000: “… I simply cannot conclude, with the information I have today, that we have enough confidence in the technology and the operational effectiveness of the entire NMD system to move forward to deployment. Therefore, I have decided not to authorize deployment of a national missile defense at this time.”  President Bill Clinton, at Georgetown University, September 1, 2000.

(2) March 18, 2003:  “Effectiveness is in the 90% range.[1]   Edward Aldridge, Undersecretary of Defense for Acquisition, Technology and Logistics.

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A Three-Stage Two-Stage GBI Interceptor (February 2, 2016)

One thing that was surprising (to me, at least) about Missile Defense Agency (MDA) Director Admiral James Syring’s January 19 2016 presentation at the Center for Strategic and International Studies was his description of the MDA’s planned two-stage version of the Ground-Based Interceptor (GBI).[1]

The MDA has long had plans to eventually incorporate a two-stage version of the three-stage GBI currently deployed in Alaska and California into its Ground Based Midcourse GMD) national missile defense system.

The idea of using a two-stage version of the GBI first came to public attention in 2006 when the George W. Bush Administration announced plans to deploy two-stage GBIs in Europe to provide an extra layer of defense of U.S. territory against Iranian ICBMs.  Although an agreement was reached in 2008 to deploy ten of the two-stage GBIs on Polish territory, in 2009 President Obama cancelled these plans in order to proceed with his European Phased Adaptive Approach (EPAA).  However, the possibility of deploying two-stage GBIs – this time on U.S. territory — was retained was retained as part of the GMD “hedge” strategy.[2]

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How Many SM-3 Block IIA Missiles? (January 25, 2016)

In a previous post, I projected the number of Aegis BMD ships, and in particular the number of ships with the “advanced” BMD capability, though 2045. I did this primarily because I was interested in the question of how many SM-3 Block IIA interceptors, which have a potentially significant capability to intercept intercontinental-range missiles, are likely to be deployed.  In this post, I turn to the question of projecting how many Aegis SM-3 block IIA interceptors the United States might eventually deploy on its ships and at its Aegis Ashore sites.

(1) Projection based on past and planned procurements.

Figure 1 shows the number of SM-3 Block IA, Block IB and Block IIA missiles in inventory based on past procurements and planned future procurements.


Figure 1.  Number of SM-3 interceptors in inventory.  Diamonds are Block I/IAs, squares are Block IBs, and circles are Block IIAs.  Numbers do not include missiles expended in tests or retired because of reaching the end of their service lives.

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How Many Aegis BMD Ships in 2040? (December 13, 2015)

For another project, I was interested in how many SM-3 Block IIA interceptors and ships capable of launching them the United States would have in the future.  This post is the result of attempting to estimate how many Aegis BMD ships the United States would have by about 2040.  In the next post, I’ll look at the numbers of interceptors.


How Many Aegis BMD Ships Today?

The U.S. Navy currently has 22 Aegis cruisers and 62 Aegis destroyers.  Five of the cruisers (CGs 61, 67, 70, 72 and 73) have a BMD capability.  Of the destroyers, all of the Flight I and Flight II ships (28 ships, DDG 51 through DDG 78) have a BMD capability.  None of the 34 Flight IIA destroyers (though DDG 112) have yet been given a BMD capability.  Thus the United States currently has 33 BMD capable ships.  These numbers are reflected in Figure 1 below.

AegisShips2015Figure 1. Planned (the chart was made in 2013) deployments of BMD capable ships as of 2015. Chart from:

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