AIM-9 Sidewinder

The AIM-9 Sidewinder is a short-range air-to-air missile. It entered service with the United States Navy in 1956 and the Air Force in 1964, and is one of the oldest, cheapest, and most successful air-to-air missiles. Its latest variants (AIM-9X) remain standard equipment in most Western-aligned air forces. The Soviet K-13 (AA-2 "Atoll"), a reverse-engineered copy of the AIM-9B, was also widely adopted.

Low-level development started in the late 1940s, emerging in the early 1950s as a guidance system for the modular Zuni rocket. This modularity allowed for the introduction of newer seekers and rocket motors, including the AIM-9C variant, which used semi-active radar homing and served as the basis of the AGM-122 Sidearm anti-radar missile. Due to the Sidewinder's infrared guidance system, the brevity code "Fox two" is used when firing the AIM-9. Originally a tail-chasing system, early models saw extensive use during the Vietnam War, but had a low success rate (8% hit rate with the AIM-9E variant). This led to all-aspect capability in the L (Lima) version, which proved an effective weapon during the 1982 Falklands War and Operation Mole Cricket 19 in Lebanon. Its adaptability has kept it in service over newer designs like the AIM-95 Agile and SRAAM that were intended to replace it.

The Sidewinder is the most widely used air-to-air missile in the West, with more than 110,000 missiles produced for the U.S. and 27 other nations, of which perhaps one percent have been used in combat. It has been built under license by Sweden and other nations. The AIM-9 has an estimated 270 aircraft kills.

In 2010, Boeing won a contract to support Sidewinder operations through to 2055. In 2021 an Air Force spokesperson said that its relatively low cost, versatility, and reliability mean it is "very possible that the Sidewinder will remain in Air Force inventories through the late 21st century".