There is one situation, at least, where you could consider taking out a DD/Escort. Lightly escorted convoys. You take out the one or two escorts and then you go for the merchies. With the escorts out of the picture you can choose more freely the ranges and angles of firing the torps, be more lenient on "silent running" procedures and even contemplaiting surface action (which would be a complete no-no with escorts around).
I'm talking about the game, of course. In a historical context ... well you know what you're supposed to do.
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