I’ve always wondered if SM-2 blk 3B didn’t have an OTH surface to surface capability with its IR guidance. That would be a big addition to AShMs if so. And of course out to the horizon most anything the USN carries can put a hole in a ship.
Does anyone know where the IR seeker came from? Was it a new development? Or is it (more likely in my opinion) an existing seeker from another system bolted on?
How does the logic work? How does the system decide which seeker has precedence over the other for guidance?
It came out of MHIP (Missile Homing Improvement Program (MHIP), which was also intended to provide a supplemental IR seeker for Sparrow. (In Sparrow, it was on the tip of the nose under a blow-off cap, with the radar seeker behind it and looking through it.)
Without going into details, the Navy's public line about MHIP in Block IIIB was that it was intended "to counter specific proliferating electronic warfare systems in existing aircraft and anti-ship cruise missile threats." So, I get the impression it was an adjunct to help the radar seeker reject countermeasures. Techniques left as an exercise for the reader.
PS: Although SM-2 Block IVA also had a side-mounted IR seeker, my recollection is that this was NOT the same MHIP seeker as in the IIIB, just the same general configuration.