I have always found the Irish Sea a good place to hunt down enemy shipping, although be careful, especially around the IOM and the northern part of the Irish sea as it contains a number of sections which have regular destroyer patrols.
The off-shoot of the area though is that alot of the Irish Sea and Bristol channel is of depths ranging from as shallow as 30m to around 90m at it's deepest points, so if you do find yourself under attack from destroyers, evasion can be a bit of a nightmare!
