dont tangle with DDs. your primary objective is to send war materials to the bottom... this means hitting those merchants.
besides... DDs are fast and maneuverable and can easily dodge any torpedo they detect. Sinking a DD that is actively hunting you, or is aware of your presence is next to impossible and counts on a great deal of luck.
futhermore there are few DDs worth more than 1900 tons, and they present very very little renown.
the best practice is to let them sail by - oblivious to your presence!
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