depends on the year of the war... One method that has been working out for me lately is to get directly ahead of the convoy with the lead escort and I going nose to nose. I order 120 meters depth and rig for silent running at 1 or 2 knots... When the lead escort passes and I'm well within his baffels I blow ballast to about 40 meters and order periscope depth and turn left or right so that I'm now 80 - 100 degrees (near perpindicular) to the convoy.
By the tim I reach periscope depth I'm in a near perfect firing position with bow AND stern tubes ready to go! Once all shots are fired I turn toward the tail of the convoy and go deep and silent.
When the escorts give up and return to their stations I surface and reintercept the convoy. BTW my attacks almost always take place at night in fair weather... Even if I have to shadow them for several days to await a weather change
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