The Rolling Airframe Missile is a point defense weapon developed jointly by the US and Germany to provide close-in defense to surface ships against anti-ship cruise missiles.
By taking the body of a Sidewinder missile, and combining it with the seeker system of the Stinger missile, development costs were kept to a minimum. The launcher is cued to the target by the ships radar, but the missile is a fire-and-forget system. A passive radio frequency seeker detects the anti-ship missile’s seeker radar or radar altimeter, and directs the RAM to the general vicinity of the target. As the RAM approaches, its passive infrared seeker head locks on and guides the missile to impact. The RAM has a couple advantages over the older Phalanx Mk15 CIWS. It has a significantly longer range than the CIWS, and it has a 21 round launcher, giving it more engagements before reloading than the CIWS. There is also an 11-round launcher based on the radar and mount of the Phalanx in development.
The latest versions of the RAM can engage helicopters, aircraft, and surface targets. The last bit, surface targets, is becoming increasingly important, as the Navy is very concerned about ships being swarmed by small boats.