The Standard Missile-6 (SM-6) is a multi-mission missile capable of antiair warfare, terminal ballistic missile defense, and antiship strike roles. It uses a blast-fragmentation warhead to engage these threats in the endo-atmosphere. The U.S. Navy has also upgraded the SM-6 to perform strike missions. Its tri-mission capability also presents opportunities for the Navy to arrange more efficient weapon loadouts onboard its guided missile ships. In the words of a former Missile Defense Agency director, the versatile SM-6 is likely to be “the workhorse for Navy cruise missile defense and ballistic missile defense for a very, very long time.”¹

SM-6 Development

After the development of the SM-2 Block IV, the Navy turned its attention to the development of an active-radiofrequency seeker to continue to expand its capability for over-the-horizon engagement.² By 2003, the Navy had settled on what would become the SM-6, which at the time was referred to as the Extended Range Active Missile (ERAM).³ The ERAM or SM-6 was designed as a key pillar of the emerging NIFC-CA concept, as its active seeker “uncouples the hard connection and dependence between the ship and the interceptor.”⁴

The Joint Requirements Oversight Council formally approved the SM-6 acquisition program in 2004 and designated it as a Major Defense Acquisition Program (MDAP).⁵ In June 2008, the SM-6 conducted its first Guided Test Vehicle (GTV) launch at White Sands Missile Range. The SM-6 reached a full rate production decision in FY 2013 and first deployed in November 2013 aboard the USS Kidd (DDG-100).⁶Its tri-mission capability also presents opportunities for the Navy to arrange more efficient weapon loadouts onboard its guided missile ships. In the words of a former Missile Defense Agency director, the versatile SM-6 is likely to be “the workhorse for Navy cruise missile defense and ballistic missile defense for a very, very long time.”

In FY 2014, the Navy commenced development of the SM-6 Block IA, which incorporates unspecified product improvements to the Block I missile.⁷ In August and November 2014, the Navy conducted land-based launches of two preproduction Block IA, successfully intercepting overland cruise missile targets.⁸ Block IA operational testing was delayed by two failures during developmental testing in August and November of 2016, successfully completing developmental tests in June 2017. Operational testing of the SM-6 Block IA began in September 2017 with two successful flight tests and is slated to wrap up in FY 2018.⁹

The Navy continues to ramp up its purchases of the SM-6, signaling an interest in phasing out older SM-2 air defense interceptors. In the 2019 National Defense Authorization Act, the Navy received congressional authority to sign a multi-year procurement agreement for 625 SM-6 interceptors over the next five years.¹⁰

Testing

During the first Control Test Vehicle (CTV) test in January 2009, the SM-6 failed because its tactical seeker battery squibbed, causing the mission computer in the missile to fail. An August 2009 retest resolved the issue in a non-intercept test.

A series of failures in development and operational testing in 2010 paused the SM-6 program temporarily. In one failure, the missile failed to communicate with the ship due to a software issue (later resolved by changes to the software). A fuze software design error caused two more failures, resulting in a redesign.¹¹ In July 2011, SM-6 successfully completed seven of 12 attempted intercepts, which concluded the missile’s Initial Operational Test and Evaluation (IOT&E) phase.¹² The Director of Operational Testing and Evaluation (DOT&E) assessed that issues with the missile fuze, likely relating to the Mk 54 Safe-Arm Device, caused two of the failures. It attributed two other failures to hardware issues caused by debris from the insulation in one of the missile’s antenna. A problem with the missile navigation system caused the final failure.¹³ In 2012, the Navy conducted wind tunnel testing on the antenna debris issue. Later tests have not demonstrated the same deficiency, leading the DOT&E to assess the issue as resolved in 2016.¹⁴ The Navy concluded the Safe-Arm fuze issues were the result of a testing anomaly in 2013.¹⁵

While the SM-6 deployed in November 2013, it maintained a “classified performance deficiency” observed by the DOT&E since FY 2013.¹⁶ As of the FY 2017 DOT&E report, the Navy had yet to conclusively resolve the issue, though it has developed a software improvement to mitigate its effects in SM-6 Block I missiles. Testing of the Navy’s software solution revealed more classified concerns for DOT&E with both the missile’s TDD and active seeker.¹⁷

Specifications

The body of the SM-6 combines the solid rocket booster and dual thrust rocket motors of the SM-3 series, the airframe of the SM-2 series, and the seeker and nosecone of an Advanced Medium-Range Air-to-Air Missile (AMRAAM).¹⁸

Within the Standard family, one unique feature of the SM-6 is its active seeker for terminal guidance, adapted from the AMRAAM missile. The AMRAAM seeker operates in the X-band, giving it greater resolution than shipboard SPY radars. Since the SM-6 is a larger airframe than the AMRAAM, the seeker inside the missile is also a bit larger.¹⁹ In addition to the active seeker mode, the SM-6 can also operate in a semi-active mode like older SM-2 missiles.

This active terminal seeker gives the SM-6 a number of advantages. For one, active homing also permits more simultaneous engagements, as SM-6 does rely on a ship’s finite number of onboard target illuminators. More critically, an active seeker allows the missile to engage targets beyond the range of shipboard radars, which are limited by power output and the curvature of the earth.  The over-the-horizon intercept capability of the SM-6 is what makes it a key pillar of the Navy Integrated Fire Control-Counter Air (NIFC-CA) concept. When integrated with other sensors through networks like the Cooperative Engagement Capability (CEC), SM-6 can conduct engagements beyond the range of any prior air defense interceptor, and set a record for the longest range antiair warfare engagement during a test in 2016.²⁰

According to MDA, the SM-6 has a different ordinance section than the SM-2 Block IV.²¹ Other sources suggest that the, the SM-6 uses the same warhead and TDD, potentially suggesting that changes are relatively minor.²²

The warhead for the SM-6 is designed for antiair missions, which may reduce its capability against larger surface targets in its antiship role. Dedicated antiship, such as the Harpoon, have a warhead weighing over 200 kg, whereas the SM-6’s warhead weighs only 64 kg. Although the SM-6’s speed adds kinetic energy to its impact, its blast fragmentation warhead may not sink larger, more hardened warships. According to analyst James Holmes, the more likely outcome of an SM-6 strike against a surface combatant is a “mission kill,” where the missile temporarily disables a target, rather than sinking it outright.²³

SM-6 Deployment and Upgrades

The first version of the Standard Missile-6 became operational in December 2014 and, in January 2015, the Navy authorized the expansion of its use from five to more than 35 ships by certifying its use on non-Baseline 9 ships.²⁴

In 2015, the Navy tested the first upgrade to the missile known as either the Dual I or Increment I. The SM-6 Dual I can intercept both cruise missiles and ballistic missiles in their terminal phase.²⁵

As of May 2015, Raytheon completed delivery of 180 Standard Missile-6 interceptors. The U.S. Navy plans to eventually purchase 1,800 of the missiles.²⁶ The United States is currently the only nation fielding the missile, but Capt. Michael Ladner, program manager of the surface ship weapons office in the Program Executive Office for Integrated Warfare Systems (PEO IWS 3.0), suggested that six international navies have reached out to discuss purchasing the interceptor.²⁷

In 2015, the Missile Defense Agency Director, VADM James D. Syring, testified in 2015 that an SM-6 Increment 2 would be certified and operational by 2018, though he did not specify what the upgrades will add to the system.²⁸

On January 10, 2017, it was reported that U.S. government cleared the SM-6 for international sale.²⁹ Initial reports suggest Australia, Japan, and South Korea are among likely international buyers because of their purchase of Baseline 9 Aegis systems. In its 2019 defense budget, Japan announced its intent to purchase SM-6 for both its naval forces and to equip its future Aegis Ashore sites.³⁰

Strike Capabilities

Because of its blast fragmentation warhead and terminal guidance systems based on GPS, multiple commanders in the Navy have also suggested that the SM-6 Dual I could be used to strike land-based targets and even provide an offensive capability against other fleets. ³¹

In February 2016, Secretary of Defense Ash Carter revealed the U.S. Navy’s intention of further upgrading SM-6 to be able to perform anti-ship strike missions:

“I want to talk to you today about the SM-6, with which we are going to create a brand-new capability.

Now, you know the SM-6. You launch it from surface ships. It’s a fantastic surface-to-air weapon; highly maneuverable, aerodynamically, and can stop incoming ballistic and cruise missiles that were trying to attack one of our warships. Can do it in the atmosphere, has very low altitude, acquire them, attack them, kill them. It’s one of our most modern and capable munitions.

I’m announcing today new capability for the SM-6. We’re modifying the SM-6, so that in addition to missile defense, it can also target enemy ships at sea at very long ranges. This is a new anti-ship mode. It makes the SM-6 basically a twofer. Can shoot down airborne threats. And now you can attack and destroy a ship at long range with the very same missile.

By taking the defensive speed and maneuverability that’s already in our Aegis destroyers’ vertical launch cells, and leveraging them for offensive surface warfare lethality, that makes it a potent new capability for you, surface warfare professionals. It’s also a good deal for the taxpayer, because they’re getting two capabilities in one missile.

We know this works. We actually tested it secretly last month, and it worked.”³²

In that test, which took place in January 2016, the USS Reuben James (DDG-245) reportedly fired an SM-6 at a target ship, sinking it.³³ Nonetheless, there are reasonable questions about the role of SM-6 in future surface warfare. Its smaller warhead limits the SM-6’s capability against larger surface ships. Because it has been designed for demanding antiair and ballistic missile defense missions, SM-6 is also relatively more expensive than other Naval surface warfare weapons at $3.5-$4 million per missile.³⁴

In principle, the SM-6 might evolve further, to acquire a land-attack role.³⁵