AIM-9 Sidewinder

Sidewinder Missile
Sidewinder Missile

The AIM-9 Sidewinder is a heat-seeking, short-range, air-to-air missile carried by fighter aircraft. It is named after the Sidewinder snake, which also detects its prey via body heat. The Sidewinder was the first really effective air-to-air missile, widely imitated and copied. Its latest variants remain in active service with many air forces.



Early development

Developed by the US Navy starting in the late 1940s, the Sidewinder introduced several new technologies that made it simpler and much more reliable than its Air Force counterpart, the AIM-4 Falcon. After terrible experiences with the Falcon in the Vietnam War, the Air Force replaced its Falcons with Sidewinders.

The primary advantage to the Sidewinder was its use of a very sophisticated detection/guidance system. During WWII the Germans had experiments with infrared guidance systems in a large missile known as the Enzian but were unable to get it to work reliably. The system used an IR detector mounted in a small steerable telescope, and used a vane in front of the mirror to tell on which side of center the target was in order to guide. By continually trying to turn the missile body toward the current direction of the telescope, the missile would guide toward the target using what is known as a pure pursuit.

The Sidewinder improved on this in a number of ways. The first was to replace the "steering" mirror with a system using a mirror that was rotating around a shaft pointed out the front of the missile, with the detector mounted in a fixed location in front of it (not to the mirror). Instead of attempting to track the target in the mirror, the IR sensor would see the target as brief flashes as the mirror lined up with the target. By knowing where the flash was as the mirror spun, the direction (radially) to the target was also known. In addition this system could track the angle-off to the target in a clever manner. If the target was further to the side of the field of view, the flash seen in the detector would be shorter due to the mirror's higher rate of motion at the outside.

Finally this sort of signal made the tracking system both simpler and much better. Instead of simply pointing the missile at the target (which is inefficient) the guidance system, the Sidewinder "remembered" each flash's direction and time. By attempting to zero out the changes, instead of the difference between the detector and missile angles, the Sidewinder flew a course known as proportional pursuit, which is much more efficient and makes the missile "lead" the target.

However this system also requires the missile to have a fixed angle of flight. If the missile spins at all, the timing based on the speed of rotation of the mirror is no longer accurate. Correcting for this spin would normally require some sort of sensor to tell which way is "down" and then adding control inputs to correct it. Instead the Sidewinder engineers came up with a very clever solution. Small control surfaces were placed at the rear of the missile with spinning disks on their outer surface. Airflow over the disk would spin them to a high speed, and if the missile started to roll, the gyroscopic force of the disk would drive the control surface into the airflow and produce the opposite control input. Thus the Sidewinder team replaced a potentially complex control system with a small bit of metal.

Service entry

A prototype Sidewinder, the XAAM-N-7 (later AIM-9A), was first fired successfully in September 1953. The initial production version, designated AAM-N-7 (later AIM-9B), entered operational use in 1956, and has been improved upon steadily since. The first combat use of the Sidewinder was in 1958 with the air force of the Republic of China on Taiwan. During that period of time, the ROC was engaged in air battles with the People's Republic of China over the Taiwan Strait. The United States provided a few dozen Sidewinders to ROC forces, which used them to great effect against PRC MiG-15s, adding a new element to an air war which had formerly been fought only with guns.

The Taiwan Strait battles inadvertently produced a new derivative of Sidewinder: shortly after that conflict the Soviet Union began the manufacture of the K-13/R-3S missile (NATO reporting name AA-2 'Atoll'), a reverse-engineered copy of the Sidewinder. It was reportedly made possible after a Taiwanese AIM-9B hit a Chinese MiG-15 without exploding, and served as a "university course" in missile design for Soviet engineers. The K-13 and its derivatives remained in production for nearly 30 years.

Although originally developed for the USN, the Sidewinder was subsequently adopted by the USAF as the GAR-8 (later AIM-9E). During the 1960s the USN and USAF pursued their own separate versions of the Sidewinder, but cost considerations later forced the development of common variants.

The Sidewinder subsequently evolved through a series of upgraded versions with newer, more sensitive seekers with various types of cooling and various propulsion, fuse, and warhead improvements.

Although each of those versions had various seeker, cooling, and fusing differences, all but one shared infrared homing. The exception was the US Navy AAM-N-7 Sidewinder IB (later AIM-9C), a Sidewinder with a semi-active radar homing seeker head developed for the F-8 Crusader. Only about 1,000 of these weapons were produced, many of which were later rebuilt as the AGM-122 Sidearm anti-radiation missile.

All-Aspect Sidewinders

AIM-9L / AIM-9M / AIM-9M-7

The next major advance in IR Sidewinder development was the AIM-9L ("Lima") model, introduced in 1978. This was the first "all-aspect" Sidewinder with the ability to attack from all angles, including head-on. In its first combat uses by Israel over Lebanon and by Britain during the Falklands War, the "Lima" reportedly achieved a kill ratio of around 80%, a dramatic improvement over the 10-15% levels of earlier weapons. In both cases, the users' opponents had not developed any tactics for the evasion of a head-on missile shot of this kind, making them all the more vulnerable.

The subsequent AIM-9M ("Mike") has the all-aspect capability of the L model while providing all-around higher performance. The M model has improved defense against infrared countermeasures, enhanced background discrimination capability, and a reduced-smoke rocket motor. These modifications increase its ability to locate and lock on a target and decrease the missile's chances for detection. Deliveries began in 1983. The AIM-9M-7 was a specific modification to AIM-9M in response to threats expected in the Persian Gulf war zone.


Now entering service is the AIM-9X, a new variant with an imaging infrared focal plane array seeker with claimed 90 off-boresight capability, compatibility with helmet-mounted sights (the new U.S. JHMCS, Joint Helmet-Mounted Cueing System), and a totally new thrust-vectoring system replacing the traditional control surfaces. It retains the same motor and warhead of the "Mike," but its lower drag gives it improved range and speed.


Missing image
AGM-122A SIDEARM being loaded onto an F-14 Tomcat

The Sidewinder was also adapted into a new missile, the AGM-122A Sidearm, which is an Anti-radiation missile utilizing an AIM-9C guidance section modified to detect and track a radiating ground-based air defense system radar. The target detecting device is modified for air-to-surface use, employing forward hemisphere acquisition capability. Sidearm stocks have apparently been expended, and the weapon is no longer in the active inventory.


The Sidewinder is the most widely used air-to-air missile in the West, with more than 110,000 missiles produced for 27 nations excluding the United States. It has been built under license by other nations (including Sweden, which builds it under the local designation Rb24). The AIM-9 is one of the oldest, least expensive and most successful air-to-air missiles.

It has been said that the design goals for the original Sidewinder were to produce a reliable and effective missile with the "electronic complexity of a table model radio and the mechanical complexity of a washing machine" -- goals which were well accomplished in the early missiles.

General characteristics (AIM-9L)

  • Length: 2.85 m (9 ft 4.2 in)
  • Wingspan: 630 mm (24.8 in)
  • Diameter: 127 mm (5 in)
  • Launch weight: 91 kg (190 lb)
  • Speed: Mach 2.5
  • Range: 18 km (11.3 mi)
  • Guidance: infrared homing
  • Warhead: 9.4 kg (20.8 lb) annular blast-fragmentation
  • Contractor: Raytheon Corporation; Ford Aerospace; Loral Corp.
  • Unit cost: $84,000 US

See also


  • Babcock, Elizabeth (1999). Sidewinder – Invention and Early Years. The China Lake Museum Foundation. 26 pp. A concise record of the development of the original Sidewinder version and the central people involved in its design.

External links

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