So it is at least plausible.
I said that they surely had military trained in that sort of thing. Actually they even seem to have a 1st Underwater demolitions Unit, so...
It's getting those people to the Baltic that seems trivial to me. That does not mean I am accusing them, but that means they are on my list of suspects.
Not accusing the SeALs just the force I'm most familiar with.
A pipeline is impossible to guard so it's so so easy, it's a cakewalk. The real challenge is the impunity, you don't want to get accused like eg Allended accused CIA of blowing up its pipelines in Chile (gasoductos y olioductos) and the train line. It's a one-dimensional structure that is vulnerable along the entire distance, and more valuable the greater the distance it covers, so more valuable as it is more vulnerable.
Really to protect a one-dimensional resource conveyor, you need retal. There's nothing else. Everybody talks about protecting themselves, yeah and what wear a helmet to cross the street? No, no helmets! Yeah then make the pipeline's steel a meter thick, to protect it.
Retal.
America does that, when terrorists blow up its pipelines in Iraq for instance, they hunt them down and make them regret doing so. Not say they're sorry, make sure it turns out to have been a bad decision in hindsight. Those pipelines don't need to be any thicker. It's the thickness of the initiator's skull that must be overcome.
It's nothing. Not a whole lotta guards from the Kremlin with their evil faces like movie bad guys (they're never not the bad guy) the whole time watching over the pipeline, let me tell you.