The RIM-116 Rolling Airframe Missile (RAM) is a small, lightweight, infrared homing surface-to-air missile in use by the German, Japanese, Greek, Turkish, South Korean, Saudi Arabian, Egyptian, Mexican and US Navies. It was intended originally and used primarily as a point-defense weapon against anti-ship missiles. As its name indicates, RAM rolls as it flies. The missile must roll during flight because the RF tracking system uses a two-antenna interferometer that can measure phase interference of the electromagnetic wave in one plane only. The rolling interferometer permits the antennas to look at all planes of incoming energy. In addition, because the missile rolls, only one pair of steering canards is required. As of 2005, it is the only U.S. Navy missile to operate in this manner.
The Rolling Airframe Missiles, together with the Mk 49 Guided Missile Launching System (GMLS) and support equipment, make up the RAM Mk 31 Guided Missile Weapon System (GMWS). The Mk-144 Guided Missile Launcher (GML) unit weighs 5,777 kilograms (12,736 lb) and stores 21 missiles. The original weapon cannot employ its own sensors prior to firing so it must be integrated with a ship's combat system, which directs the launcher at targets. On U.S. ships it is integrated with the AN/SWY-2 Ship Defense Surface Missile System (SDSMS) and Ship Self-Defense System (SSDS) Mk 1 or Mk 2 based combat systems. SeaRAM, a launcher variant equipped with independent sensors derived from the Vulcan Phalanx CIWS, is being installed on Littoral Combat Ships and certain Arleigh Burke-class destroyers.