Well yes, MAD did work mostly with some near miscalculations.
MAD works on symmetry. US\RU were equivalent enough in their nuclear arsenal for it to work.
I think robotic long range stealthy torpedo goes against that symmetry.
The russians said something about it being an answer to the ballistic missile shield program,
But that still sounds like apples to oranges.

Developing new systems is one thing, deploying a completely bew strategic wapon system
is not something a country does without a long hard analysis about what it means in
terms of relations with the rest of the world.
Maybe it is just a design and not an active development program.

To me it looks like a hyper expensive new toy (unlike ballistic missiles),
that will require the same care and protection like the missiles.
Why not put money in ballistic missile shield program like the americans?
Or modernize the existing nuclear stockpile like the americans?
Or use the money to buy more power in europe, see the plan for russin company to build a reactor for finland.
May be russia wanted it's own JSF or LRS-B money burning program.

Sing while you may
- The Legendary Pink Dots