with a pair of semi-active radar homing underwing
Skyflash missiles. at the White Sands Missile Range, New Mexico 1982.Early air-to-air missiles used
semi-active radar homing guidance, that is the missile used the radiation produced by the launching aircraft to guide it to the target. The latest generation of BVR missiles use a combination of semi-active and active radar. The first such missiles were relatively simple
beam riding designs. The Sparrow 1 mounted on the US Navy's
Skyknight became the first operational BVR missile in 1954. These primitive BVR missiles were soon replaced by missiles using
semi-active radar homing (SARH). This is where the launching aircraft's radar is
"locked" onto the target in a single target track (STT) mode, directing radar energy at the target that the missile seeker can "see" as it reflects off the target. The radar antenna must "illuminate" the target until impact. Missiles like the
Raytheon AIM-7 Sparrow and
Vympel R-27 ''(
NATO designation AA-10 'Alamo')'' home in on the reflected radiation, much as a
laser-guided bomb homes in on the reflected laser radiation. Some of the longest-range missiles in use today still use this technology. An AIM-7 variant called Sparrow II was the first attempt at producing a semi-active radar homing missile, however the first air-to-air missile to introduce a terminal active seeker operationally was the AIM-54 Phoenix carried by the
F-14 Tomcat, which entered service in 1972. This relieved the launch platform of the need to illuminate the target until impact, putting it at risk. The Phoenix and its associated Tomcat radar, the
AWG-9 was capable of multiple track and launch capability, which was unique to the Tomcat/Phoenix until the advent of AMRAAM in 1991. Newer
fire-and-forget type missiles like the
Raytheon AIM-120 AMRAAM and the Russian
R-77 (
NATO reporting name AA-12 "Adder") instead use an
inertial navigation system (INS) combined with initial target information from the launching aircraft and updates from a one or two-way data link in order to launch beyond visual range, and then switch to a terminal homing mode, typically
active radar guidance. These types of missiles have the advantage of not requiring the launching aircraft to illuminate the target with radar energy for the entire flight of the missile, and in fact do not require a radar lock to launch at all, only target tracking information. This gives the target less warning that a missile has been launched and also allows the launching aircraft to turn away once the missile is in its terminal homing phase or engage other aircraft. The very longest-range missiles like the
Hughes (now Raytheon)
AIM-54 Phoenix missile and
Vympel manufactured
R-33 (NATO designation AA-9 "Amos") use this technique also. Some variants of the Vympel R-27 use SARH for the initial guidance and then passive
infrared guidance for the final stage. This type of missile requires active guidance for a longer part of the flight than
fire-and-forget missiles but will still guide to the target even if radar lock is broken in the crucial final seconds of the engagement and may be harder to spoof with
chaff due to the dual-type guidance. == Efficiency ==