GWX 2.1 and Ports

[Jaman]

Im new to GWX so...

Is it possible in any way to sneak into a port without being detected even by armed trawlers from one mile away?.

I tried to get into Dunkirk on September 1939 on a Type IIA, i was moving at 1 knot in silent running, no periscope and with the turret well under the water, impossible to be spotted from surface (at least not from long distance). When i was at 1 mile or so from the port itself a British DD which was stationary began to move and my stealth meter went red.
I still dont know how i managed to get clear but i did after two hours of getting beat by the damn destroyer (lucky i guess).

Anyway...is there any tactic, move or even pray that i need to know to perform such a thing or should i forget about trying it and stick to high seas?.

EDIT: Oh, well, forget it. I have reach that part on the manual...geez, its on the end of it.