I think it is easier to replace rails rather than have to find another ship to replace the ones that have been sunk. Also, it would be rare for an entire rail shipment to be destroyed as opposed to an entire sea shipment being sunk. The first can offload onto trucks or if mobile can then proceed under own power. bit hard when you are 100 fathoms under.Isn't it easier for an aircraft to hit a railway which does not move and is over a long distance rather than a moving ship which if in convoy is covered by anti-aircraft fire and where the defending aircraft knows where the attack will be.
And with AMES/Radar who said the defending fighters don't know where to be?