If you look at the Baltic, I presume (But never worked there, this is a guess) * We know what ships went near the pipeline. AIS probably has it, and in that c

If you look at the Baltic, I presume (But never worked there, this is a guess) * We know what ships went near the pipeline. AIS probably has it, and in that case radar would show a ship without AIS. * We know where the pipeline is. * We don't know that something tiny like a bomb was attached. We don't know which of the passing ships did it. Same for the north sea: We know what ship/windmill/.. exists on the surface and on the floor. But I know of some divers attaching an experiment to a war ship wreck, coming back a few months later for the results, and they notice someone stole one of the ship's cannons (and these are huge and heavy). They were surprised this happened because of the sheer size of the thing, but minor theft and vandalism underwater is an everyday occurence for them.