The K-13 is an air to air missile of Soviet origin. It was a direct copy of the US AIM-9B Sidewinder air to air missile and introduced in Soviet service in the early 1960's. In the West the K-13 is better known by its NATO reporting name AA-2 Atoll. The USSR came into possession of an AIM-9B which was lodged in the tail of a Chinese MiG-17 but did not explode.

The early versions of the K-13 were a direct copy of the AIM-9B. It was copied in such detail that parts were interchangeable. Improved versions were later developed by the USSR. The K-13 is a infrared guided missile with four large wings at the rear and four smaller ones at the front. The guidance section is located at the front, the warhead in the middle and the rear half is made up of the solid propellant rocket motor.

The original version of the K-13 is the R-3S with an uncooled infrared seeker and restricts it as a tail chase missile. The much improved R-13M has a cooled infrared seeker with a much better performance but it remains a tail chase missile. The R-3R has semi-active radar homing and has an all aspect engagement capability. The radar seeker operates in the J-band and is compatible with radars such as used in the MiG-21 Fishbed.

The K-13 was a vast improvement over the earlier AA-1 Alkali. The R-3S has a maximum range of 7 km and the improved R-13M may reach out to 15 km. However, since both missiles are tail chase only the range against a target with a similar speed as the launch aircraft is only 2 and 3 km respectively.

The K-13 may be used by a wide variety of Soviet aircraft. Many aircraft that use more capable missiles in Soviet service were fitted with the K-13 in export models. The original K-13 models are used on the MiG-19, Yak-25 and early versions of the MiG-21, MiG-23 and Su-17. The R-13M is often used on the late versions of the MiG-21, MiG-23 and Su-17, as well as on the Su-25 and other newer Soviet aircraft.

The K-13 was one of the most widely exported air to air missiles in the world. During the Cold War it was used by most Soviet and Warsaw Pact aircraft and exported to most Soviet allies during the Cold War. Nowadays it is considered obsolete and has been fully replaced with more modern air to air missiles in most nations. However, it remains in widespread second line use with many nations as a weapon that arms older types of fighters and ground attack aircraft.