:hmm: Dumb luck I say.
you just have to be lucky that you find urself about a 5km range if they come to pass.
what you could do is firing up an Multi player game (LAN or Internet) start without any other and make an Generatic Mission by selecting Taskforce..make it Large , with escorts ofcourse...make the distance to taskforce medium (medium distance means that the Taskforce if bit further away before they pass you giving you the time to prepare yourself)
this is a good practice for urself so if you meet an Taskforce ingame you have a bigger chance to inflict some damages to it.
I did it once and I managed to sink 2 Dido light cruisers by launching up an Multi player game to practice...and I damaged the King George V but the escorts sunk me before I managed to sink her.
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