how do you take doen destroyers? short answer - you dont... unless its absolutely a matter of self defense, and even then... getting a solution on DE/DD can be a very difficult task.
the way you describe doing it sounds about the best method to me.
the biggest mistake of the down the throat method... people forget to zero all settings (speed, AOB, etc) before taking the shot.
but destroyers are fast and maneuverable. even with a "down the throat shot" they can turn out of the path of yoru torpedo easily most times.
if your success rate at taking out destroyers is 50% your doing pretty good IMHO.
but i also am one of those old guard skippers that feels like a DD is a waste of torpedoes.
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