Phobus; check out the first post in this thread
http://www.subsim.com/radioroom/showthread.php?t=104377
You didn't mention if your running GWX or not or what boat you had, because type IX will have a larger sig then a type VII for example. But there you will find I believe the answer to 'how he did it'.
I also would agree with any use of t/c near action usually results in bad news for your boat.