When I visited the Des-Sub Piers in Norfolk in December, I counted eight US fast-attack, one Trident, and a British fast-attack, their big new one (considerably larger than the Los Angeles-class boats nearby). Several were having "some work done" behind tarps and scaffolding around their conning towers. Now, that would be a slightly unusual model -- SSN with scaffolding.
My son in law is career Navy and a submariner. His bopat was the USS Ohio, the SSGN conversion. Was part of the conversion crew then stayed with her for a few years until he reached CPO, now he’s in the squardron and goes out to several boats.
I was able to get on the Ohioo twice with my son-in-law. Met the exec the first time and the CO the 2nd. Great experience and those Ohio boats are BIG boatd, displacing over 14,000 tons.