Not sure about RFB, sure they made it somewhat stronger. Aircraft could see subs in the right water conditions in WW2 in fairly deep water. Mostly depends on weather and water condtions. TMO can get a little unrealistic at times with planes, but that makes it fun.
Still, planes should never harm you unless you get caught in shallow water. If I get one on radar, always have plenty of time to reach the depths before they drop. Do have to be careful early war if you don't have radar.
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