DE hydrophone

[Pisces]

To make best use of your speed to gain position ahead of the target(s): Put it on your 90/270 degrees! It either slowly falls back (good, just be patient), or it shifts up to your bow(though luck, he's too fast).

But 2 knots is pretty low if the AOB is allready quite large. He's likely too fast. As suggested it is best not to dive immediatly on sight as default action. Move surfaced to extreme visible range and plot it's course while following on parallel course. Then get ahead of it and only then dive to start the attack. In your case it was the propper thing to do since you were in front of them. Or move away from them at flank. Unless they were a highspeed convoy you'd have ample extra speed available at flank.