The Standard Missile-2 (SM-2) family was developed to provide air and cruise missile defense as part of the Aegis Combat System on U.S. Navy ships. The SM-2 Blocks II, III, and IV each uses semi-active radar homing and has a blast-fragment warhead with a radar and contact fuse. 1
The familiy of SM-2 interceptors are all solid-fueled and tail controlled, designed to launch from either a Mk 41 Vertical Launching System (VLS) (see model below) or Mk 26 Guided Missile Launching System (GMLS). Most versions of the SM-2 are designed to engage high-speed, high-altitude anti-ship cruise missiles (ASCM) with midcourse guidance and radar support from the ship’s systems to help illuminate the target during the terminal intercept phase.2
Originally developed to replace the Standard Missile-1 surface-to-air missile, the Standard Missile series emphasized modularity in design to make upgrading the missiles easier as technology developed.
SM-2 Block II
The Block II upgraded the original SM-2 interceptor with a signal processor to harden the system against electronic warfare systems. It also featured an upgraded fuse and focused-blast fragment to the warhead to improve the missile’s capacity to intercept smaller, harder targets. The Block II also featured new propulsion systems for higher velocities and better maneuverability allowing it to effectively integrate more radar data for accuracy.
SM-2 Block III
The currently deployed Block III series of interceptors have a range of around 90 nautical miles. They measure 15 feet 6 inches in length and 13.5 inches in diameter and weigh around 1,558 pounds. The Block III upgrades focused on developing an advanced capability against lower altitude targets and entered service in 1981. The Block IIIA variant, which entered service in 1991, extended the range of the interceptor to even lower altitudes than the standard Block III. 3 The Block IIIB, which entered service in 1998, incorporated the infrared guidance system tested in the Missile Homing Improvement Program (MHIP) to complement the system’s radio frequency terminal homing systems. 4 This dual capability was designed to counter developments in electronic warfare.
SM-2 Block IV
The Block IV Extended Range variant can intercept targets at 100 to 200 nautical miles. They measure 21 feet 6 inches long, 21 inches wide with their boosters, and weigh 3,225 pounds apiece. The Block IV upgrade added a limited capability for terminal ballistic missile defense to the Block II and III capabilities against aircraft and ASCMs. It entered service in 1998 and deployed on Aegis ships with Mk 41 VLS tubes. As of 2012, the Navy had an inventory of 72 Block IV interceptors. 5 The Block IV features modifications to the interceptor’s fuse and autopilot. More extensive modernization was planned for the SM-2 Block IVA, which would have featured a similar dual infrared guidance system to the Block IIIB. 6
In 2015, an unspecified number of SM-2 missiles were declared Wartime Use Only after a July 18 launch incident that damaged the USS Sullivans (DDG-68). 7 The failure of the Block IIIA caused the Navy to reexamine all of the SM-2 missiles with Mk 104 Mod 2 Dual Thrust Rocket Motors (DTRM) to determine the cause of the failure. The SM-2 is in service with the United States Navy as well as 15 other allied navies, although the United States plans to phase out the interceptor in favor of the SM-6. 8
In October 2016, the USS Mason (DDG-87) fired two SM-2 Block IV interceptors and one Evolved Sea Sparrow Missile (ESSM) in self-defense against three anti-ship cruise missiles fired by Houthi militias in southern Yemen. 9