Well, based on a radio report you only usually have information on an area where they are expected to be. If they are travelling SSW, that defines a large cone covering the area from S to SW. This can be a very large area, especially if the intercept point is far away. Secondly, I find that in SH4 (with TMO), convoys and TFs zig very often. They change course constantly, and while they might have their overall destination constant, the way they get there can be very complicated. It takes a lot of luck to actually detect and close with them. Radar can _really_ help with this. Finally, I would never just sit and wait for the intercept, rather, patrol a grid over where you expect them to be, and do so at ahead full, so that you cover the search grid as fast as possible and increase the chance of an intercept.
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