In early 2016 the U.S. Navy revealed that it had successfully modified its new SM-6 (Standard Missile 6) anti-aircraft missile so that it can hit surface ships. It was only about a year ago (May 2015) that the SM-6 went into full production. At that point over 200 had already been built or ordered for development or as initial (low quantity) production. In late 2014 there were successful several live fire tests in which SM-6 shot down aircraft, anti-ship missiles and cruise missiles under a variety of different conditions. This included the longest surface-to-air engagement (missiles shooting down target) in naval history. The distance achieved was not released, but the max range of the SM-6 is given as 240 kilometers. The new version of the Aegis fire control software was also successfully tested under realistic combat conditions. It was only in 2013, two years after receiving the first production models, that the SM-6 successfully hit an aircraft (a BQM-74 target UAV) over the horizon.
This is not the first time anti-aircraft missiles have been modified to go after surface targets. But in the past this was done mainly with land based systems against stationary land targets. The SM-6 can apparently go after moving 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-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). 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-6 took nine years to develop and was in limited production since 2011, with plans to obtain 1,200 missiles at a cost of $4.3 million each. SM-6 will replace many of the SM-2 missiles currently carried by American and Australian warships.
Meanwhile, the navy has been continuing years of improvements in the Aegis radar and fire control system that controls SM-2, SM-6, and the smaller SM-3 anti-missile version. The SM-3 can destroy ballistic missiles and low orbit satellites. Aegis equipped ships began getting version 4.0 of the Aegis anti-missile software in 2013 and the latest major upgrade (5.0) makes the anti-missile capabilities a standard feature of Aegis software. New destroyers are having anti-missile Aegis software installed as standard equipment. Much of the anti-missile capability of the original Aegis anti-aircraft system came from upgrades to the Aegis software.
The Aegis anti-missile system has had a success rate of over 80 percent in knocking down incoming ballistic missile warheads during test firings. To achieve this, two similar models of the U.S. Navy Standard anti-aircraft missile are in service, in addition to a modified (to track incoming ballistic missiles version) version of the Aegis radar system.
The RIM-161A, also known as the Standard Missile 3 (or SM-3), has a range of over 500 kilometers and max altitude of over 160 kilometers. The Standard 3 is based on the anti-missile version of the Standard 2 (SM-2 Block IV). This SM-3 missile has a shorter range than the SM-2, which can destroy a warhead that is more than 200 kilometers up. The SM-3 is optimized for anti-missile work, while the SM-2 Block IV was designed to be used against both ballistic missiles and aircraft. The SM-2 Block IV also costs less than half of what an SM-3 costs. So going after aircraft with SM-3s is discouraged unless absolutely necessary.