The Skyflash, or Sky Flash in marketing material, was a medium-range semi-active radar homing air-to-air missile derived from the US AIM-7 Sparrow missile and carried by Royal Air Force McDonnell Douglas F-4 Phantoms and Tornado F3s, Italian Aeronautica Militare and Royal Saudi Air Force Tornados and Swedish Flygvapnet Saab Viggens.
Prototype Panavia Tornado ADV aircraft with semi-recessed Skyflash missiles
Swedish Air Force JA37 Viggen with a pair of underwing Skyflash missiles
Semi-active radar homing (SARH) is a common type of missile guidance system, perhaps the most common type for longer-range air-to-air and surface-to-air missile systems. The name refers to the fact that the missile itself is only a passive detector of a radar signal—provided by an external ("offboard") source—as it reflects off the target. Semi-active missile systems use bistatic continuous-wave radar.
Figure 1. Semi-active radar homing flight path geometry.
9B-1101K, inertial semi-active homing head for R-27R missiles.