The U.S. Air Force officially declared the latest version of its Sidewinder missile (AIM-9X) ready for service. The AIM-9 is the most successful air-to-air missile ever. Developed on a shoestring as an unofficial project, the first successful launch was fifty years ago (September, 1953) and it entered service in 1956. Over 100,000 of the first three versions (AIM-9, AIM-9A and B) were built through the 1960s, although there were few differences between these three. Since then, nine more versions (or families of versions) have been developed and put into service, but none had a production run of more than 23,000 (the AIM-9N). The AIM-9X is the eleventh major upgrade. The Sidewinder scored its first kill 1958, when a Taiwanese F-86 used one to down a Chinese MiG-15 over the Taiwan straits. 

The original Sidewinder was 9.3 feet long and weighed 155 pounds. It had a range of about 3200 meters. All Sidewinders have a diameter of 127mm (five inches.) The AIM-9X is 9.4 feet long, weighs 190 pounds and has a range of over twenty kilometers. The X model has much better flight controls and electronics than the original AIM-9. The X model can turn and go after a target behind it, and see through many countermeasures. During development, it was successful in 18 of 19 test launches. The AIM-9X costs about $150,000 each, and about 10,000 are expected to be built over the next two decades. Russia and Israel have developed excellent air-to-air missiles based on the Sidewinder, and the AIM-9X version was an effort to replicate many of the new features found in those foreign missiles. However, the United States Air Force has been developing airborne radars and longer range missiles that allow most of the fighting to be done beyond visual range (BVR) of the pilot. The USAF has been successful at this, but there are still occasions where a shorter range missile like Sidewinder is needed.