As far as promotions are concerned check this thread
http://www.subsim.com/radioroom/showthread.php?t=105724. The radio can be used up to 25m under the water. If you see the convoy but the game does not allow you to report it means that your crew has not "detect" it. To do this go to the hydrophone room (Key H) rotate the wheel yourself and identify the targets manually. Once you do that you will be able to send all the reports you like. It's a silly stock SH3 Bug I'm affraid, nothing to do with GWX