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nuclear bomb pictures
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You're not
wrong but in my view, far more important than the time it takes for a nuclear explosion to propagate (and I do think a time scale on the order of ms is significant for missiles in the same tight-formation salvo, but I digress) is the fact that the destruction of a ship, particularly one built to withstand multiple nuclear explosions in close proximity, is
not an instantaneous or even millisecond-scale process. Obviously the exact details are going to be highly variable particularly related to just how we envision the ships in our personal headcanon, but in any case the time required for a ship to go from suffering several missile impacts to clearly killed is non-trivial.
I'll buy everything about near-instantaneous compute and signal times for the purposes of retargeting other salvos in the same time increment as these are presumably staggered by a much greater degree than the missiles in a single salvo, but I do think the missiles in a single salvo are close enough together that by the time those milliseconds elapse, they will all have hit or attempted to hit the target simply by virtue of covering the distance to that target in less than a millisecond. Of course one can always headcanon anything one likes, but I simply don't see a good justification for
same-salvo retargeting without making a lot of leaps beyond what seems apparent in the actual game. Again, other-salvo retargeting in the same increment is perfectly fine.
Others have raised excellent points as well, and certainly game mechanically I don't think same-salvo retargeting is needed as the existing mechanic introduced interesting decisions regarding use vs. conservation of ordnance which is a good thing even if some players die a little bit inside when they "waste" a missile.