[leovampire]

Torpedo's and scopes but the water has to be on the calmer side but not planes.
If you leave the AI Visual to it's normal levels in sensativity but lower the min height to -0.4 they will see your scope when your close to them and torpedo's at the last second. But the DD's tend to go looking for you in that direction the torpedo comes from and sometimes they advoid the torpedo with a quick speed up and turn. If they see it first the whole convoy goes into a zig zag before the torpedo hits a ship.

Again time of day is a factor too because at night they tend not to see them until they are right there at the hull.

But I found that if you give a plane a type of radar set so that they can pick up a scope they send planes out at night time and in cloudy weather to look around. So there is an upside and down side to all of it.