I am skeptical of this. Not that the U.S. blew it up - that much is obvious. Or, at least… we were aware of who was blowing it up on our side.
There are a few reasons. First - a torpedo will potentially leave behind evidence. This is why I suspect divers/remote with rather simple charges. The more things to potentially find and trace back, the worse the operation is.
Torpedoes also don't have an easy way of identifying the target in a passive manner.
Pipelines tend to have accoustic monitoring devices on them. Some run through farm land outside of town, and if you start tapping on an exposed section or digging too close to one, a helicopter will come find you.
If you've ever played a quality sub simulator, you know the horrifying sound of a torpedo's terminal guidance as it closes in, and if you've ever been in a vessel below the water line that's had a torpedo's terminal guidance sonar pinging away nearby, that shit hits the hull like a hammer.
It would be rather interesting if some Gazprom techs have recordings of torpedoes homing in right before blowing up.
Which is also very doubtful, because every hydrophone in the region would pick that up and/or the sound of the torpedo's motor.
I'm not saying it is impossible - but splashes followed by the hissing of monopropellant engines tends to turn heads in sonar rooms. Sonar pings are an act of war as they are often used to resolve an accurate firing solution.
It would most probably be remote vehicle or divers. 500lbs of TNT is around 250lbs of torpex, so you'd probably need a vehicle of some sort if divers were being used.
This is exactly the kind of operation navy seals train for and why we have special forces bays/packages for Virginia and 688I class boats.
I would like to ask our military, however, where the declared war from Congress is. The President may be the commander in chief, but Congress has the exclusive authority to declare war. Such an act would be a violation of the war powers act.
Which does bring up the possibility it was someone else planting the explosives and pushing the button. Mercenaries are a thing, and even the poles can figure out how to use a claymore 30% of the time.