The Sidewinder was quickly
reverse-engineered as the
K-13 (also called
R-3 or Object 300) and entered limited service only two years later in 1960. This was followed by the improved
K-13A (
R-3S, Object 310), which entered service in 1962. The R-3S was the first version to enter widespread production, in spite of a very long seeker settling time on the order of 22 seconds, as opposed to 11 seconds for the original version. The R-3S was seen by the West in 1961 and given the NATO reporting name '''AA-2A 'Atoll''''. Minimum engagement range for the R-3S is about one kilometre. All K-13 variants are physically similar to Sidewinder, sharing the 5 inch (127 mm) diameter. Subsequent examination of AA-2 missiles captured by NATO forces showed that parts from an AIM-9 could be interchanged with parts from an AA-2, and either combination would still work. In 1962, work started on a
semi-active radar homing (SARH) version for high-altitude use, the
K-13R (
R-3R or Object 320) with 8 km range, similar to the little-used
US Navy AIM-9C Sidewinder (carried by the
F-8 Crusader). This took longer to develop, and while its first launches were in 1963, it did not enter service until 1967, alongside the radar required for it, the RP-22S, on the
MiG-21S, produced from 1965. This missile was available on all subsequent MiG-21 variants. This version was designated
AA-2B by NATO. Three training versions were also developed. The
R-3U ("uchebnaya", training) was an empty missile body with a homing set, allowing pilots to get used to the aiming of the system. The
R-3P ("prakticheskaya", practice) was a complete missile without an explosive warhead. The
RM-3V ("raketa-mishen", target-missile) served as an aerial target. == Later versions ==