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Having torpedoes that do not leave a trace is better. Historically, Japanese DD did use the wakes to trace back from where the torpedoes were launched.

As far as the game is concerned, I would assume that escorts in the early years were not as good as in the latter years. So, tracing of wakes will probably not occur in the early years.

Secondly, skippers historically avoided the MK 18s due to their bad experiences with faulty ammo in the previous years. The MK 14s finally worked, so they were unwilling to use new ammo, that they were told worked, by the same people who said the same thing about the MK 14s.