track them on hydrophones from just beyond their radar range.
try to plot their positions and anticipate where they will be over a course of hours. try to outrun them so as to position your boat submerged awaiting to ambush them once you have determined a spot where you think they will eventyally be - just wait there.
try to position your boat so that it is not likely that the escorts will pass directly over you or very close to you.
i try to not upgrade to radar. it gives away your position. if you have radar on board, the best thing to do with it is turn it off.
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