by deniability I mean that you cannot be sure if this is Russia, USA or someone else. If you use depth charges, they explode in certain way and leave some debris which say "this was XXX bomb so must be Russia/USA".
This is sabotage for sure.
This is sabotage for sure.
How else could it have been done.. What about explosives being built in from day 0? Sort of like how some bridges in Europe were pre-mined during the cold war?