The latest version of the U.S. Navy RIM-175 SM-6 (Block 1A) anti-aircraft missile passed its first tests (fired from a land based facility) and after some more test firings at sea will enter production by the end of 2017. Block 1A improvements are largely about the guidance system, especially the new anti-ship capability. SM-6 entered service in 2011 and anti-ship capability was added later. The initial order for SM-6 was for 1,200 missiles and it will eventually replace all the older SM-2s (entered service in 1979) and SM-3s (an advanced version of SM-2 that shoots down ballistic missiles).
The SM-2 ER, which entered service in 1980 and was also capable of being used against ships. SM-6 has longer range and more effective guidance (and resistance to countermeasures like jamming) than the SM-2 and is meant to deal with aircraft, cruise missile and ballistic missiles. Max range of the SM-6 is given as 240 kilometers. The longer range and higher speed of the SM-6 make it particularly effective against other ships. The SM-6 is basically the existing SM-2 anti-aircraft missile with the more capable guidance system of the AMRAAM air-to-air missile, as well as general improvements in the electronics and other components.
The SM-3, which is a version of SM-2 that specializes in intercepting ballistic missiles and low-orbit space satellites entered service in 2004 and took down its first space satellite in 2008. SM-3 missiles, because they work well and are so expensive will remain in service for another decade or more.
The SM-6 is a 1.5 ton, 6.55 meter (21.5 foot) long, 533mm (21 inch) diameter missile. It has a max altitude of 33 kilometers (110,000 feet). The older SM-2 is 1.35 ton, 8 meter (26.2 foot) long missile with a max range of 190 kilometers and max altitude of 24.4 kilometers (80,200 feet). There are smaller versions of SM-2 with shorter range and meant only for anti-aircraft work.
The main change for the SM-6 is the guidance system which is self-contained and will seek out any target it comes within range of. The SM-2 uses a "semi-active" guidance system, which requires that a special targeting radar "light up" the target with a radar beam, which the SM-2 guidance system detects and homes in on. The "active" guidance system of the SM-6 is thus harder to jam and can home in on targets beyond the range of targeting radars. The SM-6 can attack anti-ship missiles as well.
The SM-1 entered service in 1967 as the RIM-66A and underwent a major upgrade (RIM-66C) to the SM-2 in the late 1970s. There were further upgrades in the 1990s that created the anti-missile RIM-161 SM-3, which is about the same size as the SM-6.