|I read in Cordesmen AAR on GWII that the Marines found SA-6 missiles with IR seeker guidance system. This upgrade of Soviet era SAM systems could bring such outdated systems to a current feasible threat level, if they work as designed. An SA-6 launched in a area of aircraft activity could reach its max altitude of 30,000+ ft and then spiral down searching for an IR signature without using its semi-active command guidance radar system. Friendly aircraft would not have a clue what hit them. (Could be the reason for our one F-15 loss in Northern Iz) If the SA-2 had this capability it would start its downward spiral IR search at about 70,000 ft.
Optical predetermination siting as used by the NVA in N Vietnam could be used as a technique for direct IR target acquisition by SA-2s,3s,6s, and IR guided SA-8s.