Yi Peng 3 crossed both cables C-Lion 1 and BSC at times matching when they broke

Well, yes, Flag of Convenience is a thing.

But there is a "but", which is that in the articles of war, the flag of a ship does have quite a few implications. E.g. when two nations are at war, stopping ships flagged as belonging to the opposition gives certain rights of stopping and searching them, blockading their passage, seizing the vessels and cargo, etc.

And the relevant characteristic in that case is the flag, not the captain's nationality: > Art. 51. Enemy character. The enemy or neutral character of a vessel is determined by the flag which it is entitled to fly.

http://hrlibrary.umn.edu/instree/1913a.htm

If you want to be formal about it, none of the countries with Baltic coastlines are formally at war.

Yes, but there is the huge other "but" that in modern use, a formal declaration of war is no longer necessary, committing acts of war is sufficient for a state of war to exist. (However, committing acts of war without a preceding declaration is of course a war crime.)

Of course this isn't really automatic and triggered by the smallest thing, both sides kind of have to "agree" to be at war, e.g. by a counter-attack, a declaration following the attack or something like that. And nobody really wants to take that bait, due to the huge consequences involved.

Yet, it is China playing with fire here, we all can be happy that none of the affected nations took them up on their "offer" of war.

Just to clarify again, this is a dry bulk / Panamax vessel. It is part of the shipping industry. At scale, it is analogous to a railroad car. In 2015 it was operating as the Avra under the flag of Greece. The foreknowledge of the Chinese government that a Russian officer would conduct hybrid operations from the vessel cannot be inferred from the circumstance. It is like thinking that someone with an American passport is an American spy.

It is quite the opposite from what you are arguing. China is responsible for the conduct of the vessels they allowed to fly their flag.

They can later claim that the crew and captain acted on their own will, without orders from the Chinese leadership. They can duly punish the captain and crew or disavow the vessel and declare them renegade, disallow them to fly their flag. But without such a declaration, a nation such as China is responsible for the conduct of their fleets, be they civilian or military. And any vessel they allow to fly their flag is part of their (in this case civilian) fleet.

Is the US responsible for any crime committed by members of ships that fly the star-spangled banner?

To some extent, yes. US law applies on US-flagged ships.

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

> A ship's flag state exercises regulatory control over the vessel and is required to inspect it regularly, certify the ship's equipment and crew, and issue safety and pollution prevention documents.

Because US law is strong in this regard, the US military is by far the largest contributor to the count. Less than 200 civilian vessels are flagged in the US; https://www.statista.com/statistics/652126/us-flag-oceangoin....

Well sure we can both make unsourced assertions all day but as far as I can see the flag state is responsible for illegal conduct of commercial vessels only insofar it has failed to meet its obligations for regulatory and legal oversight.

Well, yes. But I'd claim that having a vessel intentionally damage foreign property and then ignoring the issue and not exercising legal oversight by at least investigating what happened is such a failure in obligations.