[Jetman123]

I honestly now prefer to keep mark 10s in my rear tubes, as after a bit of experimenting (not much, mind you) it fits my playstyle. Let the convoy drift over you, pop to periscope depth, torpedo everything in sight. Then run. Let the destroyers chase you. Go at flank battery speed and then 1/3d to make them overshoot, and make lots of crazy turns to throw their depth charges off. All the while shooting mark 10s at their keel.

Lower range? Yes. Lower speed? Yes. But at short range (which most destroyers will be at when they're trying to depth charge you) none of that matters. What matters is it's more reliable for a keel shot. I've blown open a Japanese destroyer's bow right when it was chasing me, and sunk it in a single close-range shot off the keel.