there are convoys with submerged enemy AI submarines within them as an escort... they cant attack you... they cant surface... they spawn submerged and thats it. the only advantage they offer a convoy is that if you are approaching he will be more likely to hear you and therfore alert the escorts.
if you look closely you can find his periscope sticking out of the water too.
But when you receive a contact report that reports the symbol as a circle... it is under attack from a wolf pack. AI u-boats spawn on the surface, can only attack with guns, and cannot submerge. so what you end up with is a suicide squad of about 5 or 6 u-boats rushing the convoy with guns blazing... so unless you are very close, by the time you get there the only thing you will see is a few flaming escorts because by now all of the friendly AI u-boats have been sunk by the escorts.
but if you are close... you will get to participate in the attack.
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