> assuming all of these nations record the real-time location of every fishing boat, dinghy, yacht and tug-boat; and can play it back and analyze all of the data

This is a pretty safe assumption to make. The relevent authorities have this data and are certainly poring through it as we speak.

> Your next go-to idea for the failure would be Russia or the US?

Don't put words in my mouth. I did not allude to anyone in particular, just exclude the possibility of some independent group pulling this off in case the vessels behind sabotage this do not get identified very soon.

Ok, fair point.

I agree that the various coast guards are extremely competent and coordinated, and are poring over the data that they have now. I disagree that capture is inevitable unless submarine.

Capture of the individuals behind it? Perhaps not. Identifying the vessel(s) supporting the sabotage operation? Much more likely.

Possibly. I agree that it's possible, but not inevitable. That's assuming even that stopping, diving, attaching explosives was the method.

Someone upstream suggested dragging explosives along behind the boat like an anchor, detonating when detecting the steel and concrete of the pipe. Wouldn't need scuba gear, nor even to stop.

It doesn’t take much more sophistication to place these weeks ago with a timer. And a bit more tooling and you can place them and remotely detonate when needed.