Of course, visual spotting at that range might have been possible depending upon your speed and aspect to the escort (bow-on vs side-on) (calm sea would have increased your chances of being spotted as compared to somewhat rougher seas, as pointed out above). However, my bet would be that you woul probably have been spotted by their radar at that range or further in any event. I started having problems with escorts finding me on the surface even in the densest fog from about mid-1942 onward, and based on the research I did it seems likely that at least some of the escorts in any given convoy would have had radar by late 1942, so surface attacks on convoys seem to be pretty much out of the question by then.
Good luck and good hunting
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