I'm running with GWX and i usually come across a lone DD on patrol somewhere in the middle of nowhere. So that in itself isn't to strange.
And sometimes well..... 2 nights ago while playing a single mission i was running on the surface in moderate fog when directly infront of me a DD appeared firing while clearing from the fog as if he'd known where i was all the time. And this was only late 1940 !
I barely managed to submerge before it got to me and took some damage from it's deckgun but as he passed overhead his DC's set at a very shallow depth managed to get me. I went down with heavy flooding while the DD was left with it's stern on fire and 1 screw less due to the close proximity of it's own DC.
This was a fast Wham, Bam, thank you Ma'am

and certainly not the good kind. Not sure if that was realistic given the year but hey.....