This isn't exactly a secret or new information... it was pretty well known when I lived on the peninsula 10+ years ago (thus the username, Poulsbohemian...). There's a state park right near the Hood Canal bridge where it isn't uncommon to watch the submarines come and go in and out of the canal. Always a bit surreal to push your kids on the swings while watching a first strike weapon capable of destroying the world p…
No doubt surreal, but a single sub destroy the world? That piqued my interest so took a quick look and found an article [1]. This article states that "even a single vessel [submarine] could reduce as many as 288 city-sized targets into radioactive ash in less than 30 minutes." Later in the article they say that the Ohio class is capable of carrying up to 24 UGM-133 Trident II D5 submarine launched ballistic missiles.…
https://en.wikipedia.org/wiki/Multiple_independently_targeta...
Civilian infrastructure (like your house) is readily flattened by nuclear explosions but if you want to destroy nuclear launch silos, hardened command centers, tanks, etc you need to hit them pretty much head on. It's then a lot more productive to have many independently targetable warheads to hit enemy silos in a first strike or enemy conventional forces in a tactical exchange.
In practice, you'd still get massive civilian casualties given how many bases are built right next to cities. Also, submarines are second-strike weapons so they might go for "countervalue" (your house).