Is it doable with submarines? What would you do, torpedo the pipes?

Assuming you want to plant charges, I've seen mini-subs attached to bigger submarines, but it was a movie (Red October), so no idea if that's really a thing.

Otherwise, what do you do? Can divers be deployed from a submarine?

There are subs specifically designed for these kind of special operations.

https://en.wikipedia.org/wiki/USS_Jimmy_Carter

Also the BS-136 Orenburg, among others. Both Russia and America definitely have the capability.

Thank you, also to morsch and Michael, this is very interesting. Brings me memories of the Seaview TV series.

The DSRV from the book and movie is real: https://en.m.wikipedia.org/wiki/Mystic-class_deep-submergenc...

Wow, this stuff is fascinating. And the guy really has some Paint chops.

According to some experts it may have been done using mines and divers deployed from a sub. (The use of mines is apparently somewhat medieval in this context, as there are better methods for an experienced team.) Given the density of sensor networks in the area, you'd probably need a really quiet sub, something like the German Type 212 / 212A, including export models and license builds. I guess, the Russians have something similar. (Not an expert myself by any means.) So there is quite a number of candidates in the vicinity.

P.S.: With regard to these sensor networks, I guess, the "dark" surface vessels weren't big news for the military in the area.

A rusty tanker or cargo ship with a dozen mercs and a ROV is probably way cheaper and has plausible deniability compared to a navy submarine.

The destruction was a message; back off or your internet cables, gas and oil pipelines will be destroyed. Why put any more resources into the message than is necessary for propaganda purposes?