Hmmm, are you positive it wasn't a contact that your sonar man missed...or perhaps a DD drifting after a sprint (do they even use sprint and drift tactics?)?
I was able to clear Loch Ewe with some careful planning in May '41. Bagged a Southampton, its escorting destroyer, a modern tanker, medium cargo, small merchant, and a "neutral" troop ship (I don't consider you neutral if you're parked in my enemies port, lights out, carrying troops).
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