- The timing of the explosions doesn't require "multiple coordinated teams." It requires timers. Or, as is common with naval mines, an acoustic arming/triggering signal.
- Commercial diving happens several times deeper than 80m. Hundreds of meters, in fact.
- Saturation diving techniques mean a crew could be brought to the working depth inside the ship's chamber, transferred to a diving bell, dropped down to the pipeline, do their work, go back into the bell, be brought up into the ship, transferred into the ship's decompression chamber, and decompress.
- You're assuming such an operation would be based from the surface. If a nation-state was involved, who says they arrived or departed by surface ship? The Jimmy Carter is for exactly this sort of stuff. It was practically a sport for the USSR and US to tap undersea communications cables. We had the capability to do that without being undetected (including from systems that are designed to detect faults and tampering, but also deal with the cable armoring, as well as avoid very high voltages used to power in-line amplifiers) more than fifty years ago...but you think slapping some explosives on the side of a pipe is technically challenging to a nation-state, or even a commercial diving company that does oilfield work?
- You assume that explosives were planted by divers, and not, say, a submersible (see: Jimmy Carter) or ROV. In fact, you're assuming explosives were planted, and someone didn't use a smart torpedo of some sort.
One thing, though: I agree with others that it seems unlikely Russia would do this to themselves when, you know, they can just not supply gas into the pipeline.
One possibility: after Russia threatened using nuclear devices, both pipelines were blown up was either done to send a message - or as direct punishment for the fairly unprecedented threat to use nuclear weapons.
It also has the side effect of taking any 'heat' off EU politicians to cave if energy prices soar and/or if people freeze in their homes. Russian gas is for the moment very much off the table. If those pipelines can be repaired, it won't happen overnight, or cheaply.
USA likely did it to send a message to Putin and AfD (who talking about reviving it) that Nordstream is officially dead, now and forever. USA will be supplying the oil and gas to Europe, not Russia.
I was hoping that a scuba expert would come by and help out, so thank you. After all, the fastest way to get a good answer on the internet is to post a wrong answer.
Just, as a minor point, I was responding to assertions that it could only be Russia because only a submarine crew could have done it.
The idea is that this gets everyone to think about the security of other pipelines while being less risky for Russia. And gas prices rose right afterwards.
I think planted explosives makes more sense; it would leave less/no identifiable debris behind.
By the way - Baltic Sea is not an ocean.
I would suspect dragging an explosive with a rope would take a long time, enough that radar and other ships would likely notice the behavior, especially if you intend to hit the pipeline 3 times on 3 different locations. Really expensive sonar would reduce the required time, as would really precise GPS locations, but even so, from what I know, it a very time consuming activity. Still a better theory than sport diving.
Vessel positions are tracked and recorded after all.
Russia - doing it to try and place blame on US due to Biden comments in order to sow discord amongst NATO.
Poland - they have been really vocal against NS2, they have economic and political interests aligned with its destruction, they are right there .... and my buddy who works on Polish coast said that all the gas to make trimix in that area was bought up / consumed recently. He's a diver, thought it was weird as these are common gases but assumed it was because Ukraine war. Might not be related by the way.. If I was an invrstigative reporter I'd call all the gas supply / blending / diving companies in Poland and see what their oxygen, helium, and nitrogen stock looks like.
US - always possible that US and partners just said "this makes most sense to do this. It's a win worth it". Although honestly, I don't think the current admin has the cojones to do something like this. At least not without all of NATO involved. It's too brazen.
- colonel mustard with the candlestick. Somebody else
We are talking about cold water diving, at hypoxic gas depths, with usually low visibility. The dive would require several hours of decompression in the middle of a shipping lane. The density of the gas mean you can't even do mild exertion without severe risks of not returning to the surface alive. The explosions also occurred within a very short time frame (an hour if I recall) with a fairly large distance between, so you need multiple coordinated teams. And last, the weather conditions would need to be fairly specific in term of wind at those locations.
I would say its a bit like looking towards the amateur rocket community in order to explain a construct on the moon.